CSWIP 3.2 Course Material 2016

CSWIP 3.2 – Senior Welding Inspector WIS10

Training and Examination Services Granta Park, Great Abington Cambridge CB21 6AL United Kingdom Copyright © TWI Ltd

CSWIP 3.2 Senior Welding Inspector

CSWIP 3.2 Senior Welding Inspection

Introduction

WIS10

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The Course  The Senior Welding Inspector course covers a variety of subjects that somebody operating at this level will have to have a comprehensive knowledge of.  Once each subjected is presented it will be reinforced with 10 questions relating to that subject. As the examination is multi choice these questions will also be.

Course Subjects QA and QC Destructive testing Heat treatments Welding procedures Welding dissimilar Residual stress and distortion  Weldability      

    

Weld fractures Welding symbols Non destructive testing Welding consumables Weld repairs □ □ □ □

Specifications Joint design HSLA steels Arc energy and heat input

There will also be homework each night in multi choice format which will be reviewed the following day. Copyright © TWI Ltd

Course Assessment Exam after the course is completed

No continuous assessment

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CSWIP Certificate Scheme

 3.0 Visual Welding Inspector  3.1 Welding Inspector  3.2 Senior Welding Inspector  For further examination information please see website www.cswip.com

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CSWIP 3.2 Examination  The TWI Specification will be used.  To attempt the Senior Welding Inspectors Examination (3.2) you must already be a holder of the Welding Inspectors Qualification (3.1).

CSWIP 3.0 Examination Before attempting the examination, you MUST provide the following  Two passport size photographs, with your name and signature on reverse side of both.  Eye test certificate, the certificate must show near vision and colour tests. (N4.5 or Times Roman numerals standard) and verified enrolment.  Completed examination form, you can print from the website www.twi.training.com It is the sole responsibility of the candidate to provide the above. Failure to do so will delay results and certification being issued.

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CSWIP 3.2 Examination  3.2.1

 3.2.2

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CSWIP 3.2 Examination

Without radiograph interpretation

There are four sections to the examination each will require 70% pass mark for the qualification to be awarded.

70% pass mark required in all areas of examination

 Part 1 General Multi-choice 30 Questions 45 minutes

With radiograph interpretation (Optional) 70% Pass mark required in all areas of examination including radiographic interpretation before certificate can be issued. Copyright © TWI Ltd

CSWIP 3.2 Examination All of the questions from all of the sections are generated individually from a large data base so no one student has the same exam. In the case of the scenario section of 60 questions, 12 topics will be randomly generated, each with 4 questions from the 12 sections presented through the week and 12 questions directly related to the specification. The exam specification, will be required for most of the scenario and NDT questions but not for the General and weld symbol questions. Copyright © TWI Ltd

 Part 2 Scenario multi choice 60 questions 150 minutes  Part 3 Assessment of four NDT Reports 40 Questions 75 minutes  Part 4 The interpretation of weld symbols using a drawing 10 questions 30 minutes Copyright © TWI Ltd

CSWIP 3.2 Examination For candidates wishing to complete the RT supplementary examination  Theory B2: Radiographic general theory 20 multiplechoice questions 30 Minutes  Theory: Density and Sensitivity Calculations 1 hour  Practical D2: Interpretation of Radiographs  Metal Group A: Ferrous 6 Radiographs 1 Hour 30 Minutes  Metal Group B: Austenitic 3 Radiographs 45 Minutes  Metal Group C: Aluminum 3 Radiographs 45 minutes  Metal Group D: Copper 3 Radiographs 45 minutes

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Notification of Examination Results 70% Pass mark required for EVERY section of the exam

CSWIP 3.2 Renewals

5 years

10 years

Log book submittal

Renewal examination

2 copies of certificates and an identity card sent to delegates’ sponsor

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Certification Scheme for Personnel

Recognised Worldwide Copyright © TWI Ltd

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CSWIP 3.2 – Senior Welding Inspector Contents Section

Subject

1

Duties of the Senior Welding Inspector

2

Welded Joint Design

3

Quality Assurance and Quality Control

4

Codes and Standards

5

Fe-C Steels

6

Destructive Testing

1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 1.10 1.11 1.12 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 3.1 3.2 3.3 3.4 3.5 3.6 4.1 4.2 4.3 4.4 5.1 6.1 6.2 6.3

WIS10-30816 Contents

Leadership skills Technical skills Knowledge of technology Knowledge of normative documents Knowledge of planning Knowledge of organisation Knowledge of quality/auditing Man management Recruitment Morals and motivation Discipline Summary Welds Types of joint Fillet welds Butt welds Dilution Welding symbols Welding positions Weld joint preparations Designing welded joints Summary

Definitions Quality system standards Auditing and documentation Quality requirements for welding Calibration/validation of welding equipment Workshop exercise Company manuals Auditing Codes and standards Summary Steel terminology Test types, test pieces and test objectives Fracture tests Macroscopic examination

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7

Heat Treatment

8

WPS and Welder Qualifications

9

Arc Energy and Heat Input

7.1 7.2 7.3 7.4 7.5 8.1 8.2 9.1 9.2

10

10.1 10.2 10.3 10.4 10.5 10.6 10.7 10.8

11

11.1 11.2 11.3 11.4

12

12.1 12.2 12.3

13

13.1 13.2 13.3 13.4 13.5 13.6 13.7 13.8 13.9 13.10 13.11 13.12

14

14.1 14.2 14.3 14.4

WIS10-30816 Contents

Heat treatment of steel Post weld heat treatment (PWHT) PWHT thermal cycle Heat treatment furnaces Local PWHT Qualified welding procedure specifications Welder qualification

Current and voltage Arc energy or heat imput

Residual Stress and Distortion

What causes distortion? What are the main types of distortion? What are the factors affecting distortion? Distortion – prevention by pre-setting, pre-bending or use of restraint Distortion – prevention by design Elimination of welding Distortion – prevention by fabrication techniques Distortion – corrective techniques

Weldability of Steels

Factors that effect weldability Hydrogen cracking Solidification cracking Lamellar tearing

Weld Fractures

Ductile fractures Brittle fracture Fatigue fracture

Welding Symbols

Standards for symbolic representation of welded joints on drawings Elementary welding symbols Combination of elementary symbols Supplementary symbols Position of symbols on drawings Relationship between the arrow line and the joint line Position of the reference line and position of the weld symbol Positions of the continuous line and the dashed line Dimensioning of welds Indicatgion of the welding process Other information in the tail of the reference line Weld symbols in accordance with AWS 2.4

NDT

Radiographic methods Magnetic particle testing Dye penetrant testing Surface cracks detection (magnetic particle/dye penetrant): general

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15

Welding Consumables

16

MAG welding

17

MMA Welding

18

Submerged Arc Welding

19

TIG Welding

20

Weld Repairs

15.1 15.2 15.3 15.4 15.5 15.6 15.7 15.8 16.1 16.2 16.3 16.4 17.1 17.2 17.3 17.4 17.5 17.6 17.7 17.8 18.1 18.2 18.3 19.1 19.2 19.3 19.4 19.5 19.6 19.7 19.8 20.1 20.2

MMA electrodes Cellulosic electrodes Rutile electrodes Basic electrodes Classification of electrodes TIG filler wires MIG/MAG filler wires SAW filler wires

The process Process variables Welding consumables Important inspection point/checks when MIG/MAG welding

Manual metal arc/shielded metal arc welding (MMA/SMAW) MMA welding basic equipment requirements Power requirements Welding variables Voltage Type of current and polarity Type of consumable electrode Typical welding defects The process Process variables Storage and care of consumables

Process characteristics Process variables Filler wires and shielding gases Tungsten inclusions Crater cracking Common applications of the TIG process Advantages of the TIG process Disadvantages of the TIG process Production repairs In-service repairs

Appendix Appendix Appendix Appendix

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1 2 3 4

Homeworks NDT Training Reports Training Drawing Specification Questions

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Section 1 Duties of the Senior Welding Inspector

1

Duties of the Senior Welding Inspector The Senior Welding Inspector has primarily a supervisory/managerial role, which could encompass the management and control of an inspection contract. The role would certainly include leading a team of Welding Inspectors, who will look to the Senior Welding Inspector for guidance, especially on technical subjects. The Senior Welding Inspector will be expected to give advice, resolve problems, take decisions and generally lead from the front, sometimes in difficult situations. The attributes required by the Senior Welding Inspector are varied and the emphasis on certain attributes and skills may differ from project to project. Essentially though the Senior Welding Inspector will require leadership skills, technical skills and experience.

1.1

Leadership skills Some aspects on the theory of leadership may be taught in the classroom, but leadership is an inherent part of the character and temperament of an individual. Practical application and experience play a major part in the development of leadership skills and the Senior Welding Inspector should strive to improve and fine tune these skills at every opportunity. The skills required for the development of leadership include a:  

 





1.2

Willingness and ability to accept instructions or orders from senior staff and to act in the manner prescribed. Willingness and ability to give orders in a clear and concise manner, whether verbal or written, which will leave the recipient in no doubt as to what action or actions are required. Willingness to take responsibility, particularly when things go wrong, perhaps due to the Senior Welding Inspector’s direction, or lack of it. Capacity to listen (the basis for good communication skills) if and when explanations are necessary and to provide constructive reasoning and advice. Willingness to delegate responsibility to allow staff to get on with the job and to trust them to act in a professional manner. The Senior Welding Inspector should, wherever possible, stay in the background, managing. Willingness and ability to support members of the team on technical and administrative issues.

Technical skills A number of factors make up the technical skills required by the Senior Welding Inspector and these are a knowledge of:     

Technology. Normative documents. Planning. Organisation. Auditing.

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1.3

Knowledge of technology Welding technology knowledge required by the Senior Welding Inspector is very similar to that required by the Welding Inspector, but with some additional scope and depth. Certain areas where additional knowledge is required are a:    

1.4

Knowledge of quality assurance and quality control. Sound appreciation of the four commonly used non-destructive testing methods. Basic understanding of steel metallurgy for commonly welded materials and the application of this understanding to the assessment of fracture surfaces. Assessment of non-destructive test reports, particularly the interpretation of radiographs.

Knowledge of normative documents It is not a requirement for Inspectors at any level to memorise the content of relevant normative documents, except possibly with the exception of taking examinations. Specified normative documents (specifications, standards, codes of practice, etc) should be available at the workplace and the Senior Welding Inspector would be expected to read, understand and apply the requirements with the necessary level of precision and direction required. The Senior Welding Inspector should be aware of the more widely used standards as applied in welding and fabrication. For example:

1.5

BS EN ISO 15614 / ASME IX

Standards for welding procedure approval

BS 4872, BS EN 287/ BS EN ISO 9606 / ASME IX PED BS 5500 / ASME VIII

Standards for welder approval.

BS EN ISO 9000 – 2000

Standards for quality management.

Standards for quality of fabrication.

Knowledge of planning Any project or contract will require some planning if inspection is to be carried out effectively and within budget. See Section: Planning for more detailed information.

1.6

Knowledge of organisation The Senior Welding Inspector must have good organisational skills in order to ensure that the inspection requirements of any quality/inspection plan can be met, within the allocated time, budget and using the most suitable personnel for the activity. Assessment of suitable personnel may require consideration of their technical, physical and mental abilities in order to ensure that they are able to perform the tasks required of them. Other considerations would include availability of inspection personnel at the time required, levels of supervision and the monitoring of the inspector’s activities form start to contract completion.

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1.7

Knowledge of quality/auditing There are many situations in manufacturing or on a project where the Senior Welding Inspector may be required to carry out audits. See section on: Quality Assurance/Quality Control and Inspection for more detailed information.

1.8

Man management As mentioned above, the Senior Welding Inspector will have to with a team of Inspection personnel which he may well have have to liaise with customer representatives, sub-contractors Inspectors. He may have to investigate non-compliances, deal discipline as well as personal matters of his staff.

direct and work to pick. He will and third party with matters of

To do this effectively he needs skills in man management. 1.9

Recruitment When recruiting an individual or a team the SWI will first have to establish the requirements of the work. Among them would be:         

What skills are definitely required for the work and what additional ones would be desirable? Are particular qualifications needed? Is experience of similar work desirable? What physical attributes are needed? Is the work local, in-shop, on-site, in a third world country? Does the job require working unsociable hours being away from home for long periods? Is the job for permanent staff or for a fixed term? If overseas what are the leave and travel arrangements? What is the likely salary?

During subsequent interviews the SWI will need to assess other aspects of the candidates’ suitability:     

1.10

Has he the ability to work on his own initiative? Can he work as part of a team? If overseas has the person been to a similar location? What is his marital/home situation? Are there any Passport/Visa problems likely?

Morale and motivation The morale of a workforce has a significant effect on its performance so the SWI must strive to keep the personnel happy and motivated and be able to detect signs of low morale. Low morale can lead to among other things, poor productivity, less good workmanship, lack of diligence, taking short cuts, ignoring safety procedures and higher levels of absenteeism. The SWI needs to be able to recognise these signs and others such as personnel not starting work promptly, taking longer breaks, talking in groups and grumbling about minor matters.

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A good supervisor should not allow his workforce to get into such a state. He must keep them motivated by: 

 



1.11

His own demeanour – does he have drive and enthusiasm or is he seen to have no energy and generally depressed. The workforce will react accordingly. Is he seen to be leading from the front in a fair and consistent manner? Favouritism in the treatment of staff, on disciplinary matters, the allocation of work, allotment of overtime, weekend working and holidays are common causes of problems. Keep them informed in all aspects of the job and their situation. Rumours of impending redundancies or cuts in allowances etc will not make for good morale.

Discipline Any workforce must be working in a disciplined manner, normally to rules and standards laid down in the Company’s conditions of employment or relevant company handbook. The SWI must have a good understanding of these requirements and be able to apply them in a fair and equitable manner. He must have a clear understanding as to the limits of his authority – knowing how far he can go in disciplinary proceedings. The usual stages of disciplinary procedure are:      

The quiet word. Formal verbal warning. Written warning. Possible demotion, transfer, suspension. Dismissal with notice. Instant dismissal.

Usually after the written warning stage the matter will be handled by the Company’s Personnel or Human Resources Department. It is of vital importance that the company rules are rigorously followed as any deviation could result in claims for unfair or constructive dismissal. In dealing with disciplinary matters the SWI must:    

Act promptly. Mean what he says. Treat everyone fairly and as an adult. Avoid constant complaining on petty issues.

Where there are serious breaches of company rules by one or two people the rest of the workforce should be informed of the matter so that rumour and counter-rumours can be quashed. Some matters of discipline may well arise because of incorrect working practices, passing off below quality work, signing for work which has not been done, etc.

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In all such cases the SWI will need to carry out an investigation and apply disciplinary sanctions to the personnel involved. To do this:  

     

1.12

First establish the facts – by interviewing staff, from the relevant records, by having rechecks on part of the job. If any suspicions are confirmed, transfer/remove suspect personnel from the job pending disciplinary proceedings. If the personnel are employed by a sub-contractor then a meeting with the sub-contractor will be needed to achieve the same end. Find out the extent of the problem, is it localised or widespread? Is there need to inform the customer and third party inspector? Formulate a plan of action, with other company departments where necessary, to retrieve the situation. Carry out the necessary disciplinary measures on the personnel involved. Convene a meeting with the rest of the workforce to inform them of the situation and ensure that any similar lapses will be dealt with severely. Follow up the meeting with a written memo.

Summary The Senior Welding Inspector’s role can be varied and complex, a number of skills need to be developed in order for the individual to be effective in the role. Every Senior Welding Inspector will have personal skills and attributes which can be brought to the job, some of the skills identified above may already have been mastered or understood. The important thing for the individual to recognise is not only do they have unique abilities which they can bring to the role, but they also need to strive to be the best they can by strengthening identifiable weak areas in their knowledge and understanding. Some ways in which these goals may be achieved is through:       

Embracing facts and realities. Being creative. Being interested in solving problems. Being pro-active not reactive. Having empathy with other people. Having personal values. Being objective.

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Section 2 Welded Joint Design

2

Welded Joint Design This section is principally concerned with structures fabricated by welding steel plates together, examples include bridges, ships, offshore platforms, pressure vessels and pipelines, although in some cases this may involve welding curved plates together. This section introduces typical joint geometries involved in joining plates together and describes the types of weld used in these joint configurations with typical features of butt and fillet welds described. For the structure to function loads must be transferred from one plate to another and the features of welds that enable them to transmit loads are described. Finally, some examples of good and bad design practice are given.

2.1

Welds A weld is a permanent union between materials caused by the application of heat, pressure or both and if made between two faces approximately parallel is known as a butt weld.

Figure 2.1 Butt weld.

A weld made between two faces that are approximately at right angles to each other is known as a fillet weld.

Figure 2.2 Fillet weld.

For simplicity these diagrams show an arc welding process that deposits filler weld metal in a single weld pass. Typical features of a butt weld are shown in Figure 2.3 and those of a fillet weld in Figure 2.4. The weld or weld metal refers to all the material that has melted and resolidified. The heat-affected zone (HAZ) is material that has not melted but whose microstructure has been changed as a result of the welding. The fusion line is the interface between the weld metal and the HAZ.

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The root is the bottom of the weld or narrowest part and the face is the top or widest part. At the corners of the weld cross section where the weld metal joins the parent metal are the weld toes. These are at each corner of both the weld face and weld root in a butt weld but only on the weld face in a fillet weld.

a Fusion line

Weld metal

Weld toe

HAZ

Parent metal

b Figure 2.3 Typical features of a: a b

Butt weld. Double-sided butt weld.

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Figure 2.4 Typical features of a fillet weld.

The application of heat naturally causes some changes to the microstructure parent material, the HAZ shown in Figure 2.5 for a butt weld in steel with similar HAZs developed in the parent material of fillet welds. Close to the fusion line the temperature in the HAZ has been sufficient to cause microstructural phase changes, which will result in recrystallisation and grain growth. Further away from the fusion line the parent material has been heated to a lower maximum temperature and the parent microstructure is tempered.

Maximum temperature

Solid weld metal

Solid-liquid boundary Grain growth zone Recrystallised zone Partially transformed zone Tempered zone Unaffected base material

Figure 2.5 HAZs in a butt weld.

The distance between weld toes is the weld width. When the distance is between the toes at the weld cap it is the weld cap width, the distance between the toes at the root is the weld root width.

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The height of the additional weld metal in the weld cap is the excess weld metal which used to be called reinforcement which wrongly suggests that increasing this dimension will strengthen the weld. If the excess weld metal is too great it increases the stress concentration at the weld toe and this extra weld metal is called the excess root penetration. Weld width

Excess weld metal

Excess root penetration Figure 2.6 Definitions on a butt weld.

2.2

Types of joint A joint can simply be described as a configuration of members and can be described independently of how it is welded. Figures 2.7 and 2.8 show the most common joint types - butt and T joint. Other typical joint types are shown in Figures 2.9-2.11; lap, cruciform and corner joint. When designing a lap joint the overlap between the two plates needs to be at least four times the plate thickness (D = 4t), but not less than 25mm.

Figure 2.7 Butt joint.

Figure 2.8 T joint.

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Figure 2.9 Lap joints.

Figure 2.10 Cruciform Joint

Figure 2.11 Corner joint.

An alternative to a conventional lap joint is to weld the joint using plug or slot welding, shown in Figure 2.12 showing the typical lap joint can be drastically altered. The hole for a slot weld should have a width at least three times the plate thickness and not less than 25mm. In plate less than 10mm thickness, a hole of equal width to the plate thickness can be welded as a plug weld.

a

b

Figure 2.12: a

b

Slot welded lap joint. Plug welded lap joint.

Corner joints can be fitted and welded in a number of ways. The unwelded pieces can be assembled either with an open corner or closed together. The weld can be on the external or internal corner or both in a double-sided weld.

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Open

Closed

External corner joint

Internal corner joint

Double-sided corner joint

Figure 2.13 Different types of corner joints, unwelded and welded.

2.3

Fillet welds The throat and leg length of a fillet weld are shown in Figure 2.14. Throat size a is generally used as the design parameter since this part of the weld bears the stresses and can be related to leg length z by the following relationship: a ≈ 0.7z and z ≈ 1.4a. Throat a

Leg

Leg z Figure 2.14 Leg length z and throat size a in a fillet weld.

This is only valid for mitre fillet welds having similar leg lengths (Figure 2.15), so is not valid for concave, convex or asymmetric welds. In concave fillet welds the throat thickness will be much less than 0.7 times the length. The leg length of a fillet weld is often approximately equal to the material thickness. The actual throat size is the width between the fused weld root and the segment linking the two weld toes, shown as the red line in Figure 2.16. Due to root penetration the actual throat size of a fillet weld is often larger than its design size but because of the unpredictability of the root penetration area, the design throat size must always be taken as the stress parameters in design calculations.

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z a

z Figure 2.15 Mitre fillet weld.

Figure 2.16 Design throat of a fillet weld.

Convex fillet weld

Concave fillet weld

Mitre fillet weld Figure 2.17 Fillet weld cross-sections.

Actual throat

Design throat

Design throat = actual throat

Figure 2.18 Definition of design and actual throat in concave and convex fillet welds.

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The choice between mitre weld, concave and convex fillet weld needs to account for the weld toe blend. A concave fillet weld gives a smooth blend profile and a low stress concentration at the fillet weld toe. Convex fillet welds can have a higher stress concentration at the weld toe. If the fluidity of the weld pool is not controlled it is possible to obtain an asymmetrical fillet weld where the weld pool has sagged into the joint preparation and there is also a risk of undercut on the bottom weld toe (see Figure 2.19). Having a smooth toe blend is important to give better fatigue performance for fillet welds.

Figure 2.19 Fillet weld toe blends.

2.4

Butt welds The design throat t 1 of a butt weld is the penetration depth below the parent plate surface and no account is made of the excess weld metal. The design throat is therefore less than the actual throat t 2 .

Figure 2.20 Design throat t 1 and the actual throat t 2 for butt welds.

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The weld toe blend is important for butt welds as well as fillet welds. Most codes state that weld toes shall blend smoothly, leaving it open to individual interpretation. The higher the toe blend angle the greater the amount of stress concentration. The toe blend angle ideally should be between 20-30 degrees (Figure 2.21). 6mm

Poor weld toe blend angle

3mm

Improved weld toe blend angle Figure 2.21 Toe blend in butt welds.

2.5

Dilution When filler and parent material do not have the same composition the resulting composition of the weld depends largely on the weld preparation before welding. The degree of dilution results from the edge preparation and process used; the percentage of dilution (D) is particularly important when welding dissimilar materials and is expressed as the ratio between the weight of parent material melted and the total weight of fused material (multiplied by 100 to be expressed as a percentage), as shown:

D=

Weight of parent material melted × 100 Total weight of fused material

Low dilutions are obtained with fillet welds and with butt welds with multiple runs. For a single pass better dilution is obtained with grooved welds, see Figure 2.22.

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Fillet welds

Single V groove weld

Square groove weld

Figure 2.22 Effect of weld preparation on dilution and weld metal composition (for a single pass only).

2.6

Welding symbols On engineering drawings a welded joint can be represented by different means. A detailed representation shows every detail and dimension of the joint preparation with carefully written, extensive notes. It provides all the details required to produce a particular weld in a very clear manner but requires a separate detailed sketch (time consuming and can overburden the drawing). For a special weld preparation not covered in the relevant standards (eg narrow groove welding); it is the only way to indicate the way components are to be prepared for welding or brazing. 8-12°

8-12

1-3

≈R6 R6

8mm

1-4

Figure 2.23 Detailed representation of U bevel angle.

Symbolic representation using weld symbols can specify joining and inspection information and the UK has traditionally used BS 499 Part 2 which has been superseded by BS EN ISO 2553. In many welding and fabrication organisations use old drawings that reference out of date standards such as BS 499 Pt 2. BS EN ISO 2553 is almost identical to the original BS EN ISO 2553 standard on which it was based. In America AWS A2.4 is followed, while symbols for brazing are given in EN 14324.

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The advantages of symbolic representation are:    

Simple and quick to visualise on the drawing. Does not overburden the drawing. No need for additional views as all welding symbols can be placed on the main assembly drawing. Gives all necessary indications regarding the specific joint to be obtained.

Symbolic representation can only be used for common joints and requires training to understand the symbols. Symbolic representation of a welded joint contains an arrow line, a reference line and an elementary symbol. The elementary symbol can be complemented by a supplementary symbol. The arrow line can be at any angle (except 180 degrees) and can point up or down. The arrow head must touch the surfaces of the components to be joined and the location of the weld. Any intended edge preparation or weldment is not shown as an actual cross-sectional representation but as a line. The arrow also points to the component to be prepared with single prepared components.

Figure 2.24 Symbolic representation of U bevel angle.

BS EN ISO 2553 and AWS A2.4 list all the main elementary symbols, some examples are shown in Table 2.1. The symbols for arc welding are often shown as cross-sectional representations of a joint design or completed weld. Simple, single edge preparations are shown in Figure 2.25.

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Table 2.1 Elementary weld symbols.

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Key: a = b = c = d = e = f =

single V butt joint. double V butt joint. single bevel butt joint. double bevel butt joint. single sided fillet weld. double sided fillet weld.

Figure 2.25 Welding symbols for the most common joint types shown on a reference line.

These simple symbols can be interpreted as either the joint details alone or the completed weld. For a finished weld it is normal for an appropriate weld shape to be specified. There are a number of options and methods to specify an appropriate weld shape or finish. Butt welded configurations would normally be shown as a convex profile (Figure 2.26 a, d and f) or as a dressed-off weld as shown in b and c. Fillet weld symbols are always shown as a mitre fillet weld and a convex or concave profile can be superimposed over the original symbol's mitre shape.

Key:

a b c d e f

= = = = = =

single V butt weld with convex profile. double V butt weld flushed off both sides on weld face. single bevel butt weld flushed off both sides on weld face. double bevel butt convex (as welded). concave fillet weld. double sided convex fillet weld.

Figure 2.26 Welding symbols showing the weld profile for the most common joint types.

So the correct size of weld can be applied it is common to find numbers to the left or right of the symbol. For fillet welds numbers to the left indicate the design throat thickness, leg length or both (Figure 2.27).

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a7 z 10 a7 z 10

Figure 2.27 Throat and leg length dimensions given on the weld symbol for a fillet weld.

For butt joints and welds an S with a number to the left of a symbol refers to the depth of penetration. When there are no specific dimensional requirements specified for butt welds on a drawing using weld symbols, it would normally be assumed that the requirement is for a full penetration butt weld. Numbers to the right of a symbol or symbols relate to the longitudinal dimension of welds, eg for fillets the number of welds, weld length and weld spacing for noncontinuous welds.

Figure 2.28 Weld symbols showing the weld length dimensions to the right of the weld joint symbols for an intermittent fillet weld.

Supplementary symbols can be used for special cases where additional information is required (Figure 2.29). The weld all round symbols may be used for a rectangular hollow section (RHS) welded to a plate, for example. The flag symbol for weld in the field or on site can be added to any standard symbol. A box attached to the tail of the arrow can contain or point to other information such as whether NDT is required. This information is sometimes the welding process type given as a three number reference from BS EN ISO 4063, for example 135 refers to MAG welding.

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Figure 2.29 Examples of supplementary symbols.

2.7

Welding positions In weld procedure documents and engineering drawings the type and orientation of welds are often given a two letter abbreviation which defines them which can vary depending on the standard the welds are conforming to. The abbreviations here are consistent with BS EN ISO 6947 and are summarised in Table 2.2.

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Table 2.2 Welding positions.

Welding position

Figure/symbol

Abbreviation

Flat

PA

Horizontal

PB

Horizontal vertical

PC

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Welding position

2.8

Figure/symbol

Abbreviation

Vertical up, vertical down

PG/PF

Overhead

PE

Horizontal overhead

PD

Weld joint preparations The simplest weld joint preparation is a square edged butt joint, either closed or open. A closed butt joint is used in thick plate for keyhole welding processes such as laser or electron beam welding (EBW). A square edged open butt joint is used for thinner plate up to 3mm thickness for arc welding in a single pass or in thick plate for welding processes such as electroslag welding.

Square edge closed butt

Square edge open butt

Figure 2.30 Square edge butt joints.

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It is normal to use a bevel on the edges of the parent metal to be welded to allow access to the root for the first welding pass which is filled using fill passes. Single-sided preparations are normally made on thinner materials or when access from both sides is restricted. Double-sided preparations are normally made on thicker materials or when access from both sides is unrestricted. Edge preparation design includes the bevel angle (or included angle if both sides are bevelled) and also the square edges root face and root gap. In a joint where both sides are bevelled the preparation is termed a V or vee preparation (Figure 2.31). V preparations are usually used for plate of 3-20mm thickness. An alternative is a U preparation (or J preparation if only one side has the edge preparation) where the edge is machined into the shape of a U. This is used in thicker plate, over 20mm thickness, where it uses less filler metal than a V preparation joint. J or U edge preparations also require a bevel angle and root face, the gap to be defined, a root radius and land to be specified (Figure 2.32). Single-sided edge preparations are often used for thinner materials or when there is no access to the root of the weld (pipelines). If there is access to both sides of the material then a double-sided edge preparation is used, especially for thicker materials. Single and double edge preparations are shown in Figure 2.33. Included angle

Bevel angle

Root face Gap Figure 2.31 Single V bevel.

Included angle Root radius Bevel angle

Root face Gap Land Figure 2.32 U bevel.

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Single Bevel

Single J

Single V

Single U

Double Bevel

Double V

Double J

Double U

Figure 2.33 Range of single and double-sided bevel, V, J and U preparations.

2.9

Designing welded joints Weld joint design selection will also be influenced by practical issues such as the welding process used and the access required to obtain root fusion. The bevel angle must allow good access to the root and sufficient manipulation of the electrode to ensure good sidewall fusion (Figure 2.34). If the included angle is too large then heavy distortions can result and more filler metal is required. If the included angle is too small there is a risk of lack of penetration or lack of sidewall fusion. Typical bevel angles are 30-35 degrees in a V preparation (6070 degrees included angle). In a single bevel joint the bevel angle might be increased to 45 degrees.

Figure 2.34 Bevel angle to allow electrode manipulation for sidewall fusion.

The root gap and face are selected to ensure good root fusion (Figure 2.35). This will depend on the welding process and heat input. If the root gap is too wide or root face too narrow there is a risk of burn through. If the root gap is too narrow or root face is too deep there is a risk of lack of root penetration. A balance must be found and designed for; this difference in weld root size is shown in Figure 2.36. High heat input processes require a larger root face but less weld metal which reduces distortions and increases productivity. Typical values for the root face are 1.5-2.5mm and the root gap 2-4mm.

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Figure 2.35 The importance of selecting the correct root face and gap.

a

b

Figure 2.36 Root size for welding processes with different heat inputs:

a b

Low heat input. High heat input.

If the components are to be joined by an arc welding process the selected bevels need to be adequately machined to allow the welding tool to access the root of the weld. This consideration would not apply for a procedure such as EBW as shown in Figure 2.37. If using gas-shielded processes then the size of the gas nozzle may limit the ability to use a J preparation for thick section material as it would be difficult to ensure good root fusion if the welding head could not access the bottom of the weld groove and a single bevel may be needed instead (Figure 2.38).

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a

b

Figure 2.37 Preparation differences between:

a b

Arc. Electron beam welding.

a

b

Figure 2.38 Using gas-shielded arc welding:

a b

Difficulties of root access in a J preparation. Improved design using a bevel preparation.

Choosing between a J or U preparation and a bevel or V preparation is also determined by the costs or producing the edge preparation. Machining a J or U preparation can be slow and expensive. Using this joint design also results in tighter tolerance which can be easier to set-up. A bevel or V preparation can be flame or plasma cut fast and cheaply resulting in larger tolerances, meaning that set-up can be more difficult. Backing bar or strip is used to ensure consistent root fusion and avoid burn through. Permanent backing bar (rather than one removed after welding), gives a built-in crevice which can make the joints susceptible to corrosion (Figure 2.39). When using backing for aluminium welds any chemical cleaning reagents must be removed before assembling the joint. A backing bar also gives a lower fatigue life.

Figure 2.39 Using a backing bar for a butt weld.

Separate from the design of the joint and weld access to weld locations and the order in which welds are made are important. Figure 2.40 shows examples of the limitations of access in designing welded joints and gives improved designs. It is important to ensure that it is indeed possible to make welds as required by the drawing.

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Figure 2.40 Examples of improved weld designs where there is limited access.

2.10

Summary You should now:  

Be able to label the parts of a butt and fillet weld and of a V and U edge preparations. Recognise welding symbols and know what they mean.

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Outline       

Welded Joint Design Section 2

What determines joint Design? Weld features. Types of welded joints. Welding symbols. Weld positions. Weld bevels. Designing welded joints.

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Types of Welds Weld A permanent union between materials caused by heat, and or pressure (BS499).

Fillet Welds Fillet welds

Throat

Butt weld

Fillet weld Leg

Leg size Leg

Throat size

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Butt Joint Preparations

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Single Sided Butt Preparations Single sided preparations are normally made on thinner materials, or when access from both sides is restricted

Square Edge Closed Butt

Single bevel

Single V

Single-J

Single-U

Square Edge Open Butt

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2‐1

Double Sided Butt Preparations Double sided preparations are normally made on thicker materials, or when access form both sides is unrestricted

Joint Preparation Terminology Angle of bevel

Root Radius

Double -Vee

Double -Bevel

Root Face Root Gap Double - U

Double - J

Single bevel butt Copyright © TWI Ltd

Joint Preparation Terminology Included angle

Included angle

Angle of bevel Root radius

Root face Root gap Single-V butt

Root gap

Angle of bevel

Root Gap

Root Face Land

Single-J butt Copyright © TWI Ltd

What determines welded joint design? Design, fatigue life expectancy, loading types Full penetration butt weld gives better life expectancy compared to partial penetration and compound weld gives better performance than a fillet weld.

Root face

Single-U butt Copyright © TWI Ltd

What determines welded joint design? Welding process  Open root runs with SAW. (Difficult unless backing is used or closed)  Closed square edge butt joints key hole Plasma and Electron Beam. (Key hole technique used)  Thin wall S/S Dairy pipe closed square edge butt joint TIG.  Access for large welding heads U butts.  Positional welding with SAW.

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Copyright © TWI Ltd

What determines welded joint design? Material thickness  Butt welds, generally, as material gets thicker single preparations become double preparations. (Dependent on access)  Butt welds, generally as material gets thinner, root gaps close.  T joints, generally as material gets thicker, the vertical plate is prepared. (Compound weld)

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2‐2

What determines welded joint design? Quality Root penetration is guaranteed if backing is used, ceramic or a material that won’t fuse, shaped to produce a particular profile.

What determines welded joint design? Quality To ensure that root defects are minimised, back gouge and check via NDT, MPI/Dye pen.

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Access and Weld preparations Access impacts upon weld preparation

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What determines welded joint design? Welding position

Preparation for horizontal welding using the submerged Arc welding process

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What determines welded joint design? Welding position

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What determines welded joint design? Weld volume

 A U butt between 20-30% less weld volume than a V Butt.  The benefits could be reduced costs, reduced residual stress and reduced distortion.  The disadvantages of the U is the additional preparation costs of machining although fit up conditions improve. Copyright © TWI Ltd

Copyright © TWI Ltd

2‐3

What determines welded joint design? Weld volume

What determines welded joint design? Distortion control Double V butt

 A double V has less weld volume than a single V.  A double V, therefore will reduce cost, reduce distortion and stress and should guarantee higher quality.  Disadvantage of the double V, access to both sides required.

 The asymmetrical V butt, ⅓,

Distortion control Shrinkage

ଶ ଷ

is often used to

control distortion. The smaller v is completed first.

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What determines welded joint design?

Asymmetrical V butt

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What determines welded joint design? Level of penetration

Shrinkage

Full penetration

Partial penetration

The U butt has significantly less liquid metal and a more even distribution of weld metal in the upper most regions than the V butt. Therefore, greater shrinkage and distortion occurs with the V butt. Copyright © TWI Ltd

What determines welded joint design? Level of penetration

Small root face

Full penetration

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What determines welded joint design? Gas purging of pipes

Large root face

Less penetration It is much easier to regulate the gas purge if the joint is closed.

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2‐4

Nozzles Nozzles connect a pressure vessel with other components

Set-On Nozzle  Shorter nozzle is cheaper.  Easy to make groove for full or partial penetration.  Single side welding in 2G/PB position means high welder skill is required.  Through thickness stress means danger of lamellar tearing.  Can be difficult to UT especially on smaller diameters.  Mainly used for small ( ~1050°C

Austenite ( γ)

Temperature,°C

~900°C

Austenite + ferrite ( γ+α)

~700°C

Ferrite + pearlite (α )+ iron carbide)

As-rolled or hot rolled

Control-rolled or TMCP

Time Figure 7.3 Comparison of the ‘control-rolled’ (TMCP) and ‘as-rolled’ conditions (= hot rolling).

Solution heat treatment   

Rapid heating to soak temp. (100% austenite). Short ‘soak’ time at temperature. Rapid cool cooling by quenching into water or oil.

Temperature,°C

> ~1050°C

Quenching

Time Figure 7.4 Typical solution heat treatment (solution annealing) applied to austenitic stainless steels.

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Annealing Rapid heating to soak temperature (100% austenite). Short ‘soak’ time at temperature. Slow cool in furnace to ambient temperature.

 

Temperature,°C



~900°C

Time

Figure 7.5 Typical annealing heat treatment applied to C-Mn and some low alloy steels.

PWHT (C-Mn steels) 

Temperature °C

 

Controlled heating rate from 300°C to soak temperature. Minimum soak time at temperature. Controlled cooling to ~300°C.

~600°C Controlled heating and cooling rates ~300°C Soak time

Air cool

Time Figure 7.6 Typical PWHT applied to C-Mn steels.

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Weld seam

Figure 7.7 Local PWHT of a pipe girth seam.

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Heat Treatment Controlled heating and cooling to bring about desired changes in metals and alloys Objectives  Microstructural changes improve mechanical properties ie toughness, machinability, strength.  Reduce residual stress level.

Heat Treatment Section 7

Where?

Global

Local

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Copyright © TWI Ltd

Carrying Out Heat Treatment Heating & cooling bulk specimen Furnaces and ovens Gas fired Electric

Heat Treatment Electric heating mats Temperature control? Use thermocouples, optical pyrometers

Localised Heat treatment Localised heat sources Flame heating Induction heating Laser heating

Heat Treatment Equipment Furnaces and ovens Gas fired:  Special attention to environment control.  Heat from oxygen + fuel gas (methane, propane).  High concentration of oxygen may result in scaling, a neutral environment is beneficial.  Avoid heat gradients.  Radiant tube furnaces to avoid contact with combustion product. Electric furnaces:  Cleaner environment.  Expensive.

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Localised Heat Treatment  Heating and cooling a specific portion of a component, ie gear edge, case or surface hardening, weld PWHT.  Gas flames such as oxygen + methane or propane.  Induction.  Electric heating blankets.

Heat Treatment Cycle Temperature Soaking temperature

Important parameters  Heating rate.  Soaking temperature.  Soaking time (1h/25mm).  Cooling rate. Time

Heating

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Soaking

Cooling

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7‐1

Types of Heat Treatment  Annealing.  Normalising.  Recovery and re-crystallisation.  Stress relief.  Quenching and tempering.  Precipitation hardening.

Heat Treatment Temperatures oC

Welds & parent metals

Homogenizing and hot working Austenite

Annealing

Acm

910 Normalizing A3

Normalising

Annealing

727

Recovery and recrystallization

Parent metals 600

Recovery & recrystallisation Stress relief & PWHT

A1

PWHT and PWHT Stress Relieve

Phase change to austenite

No phase change

500 0.022

0.77

2.0

Carbon content in weight %

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Full Annealing - Steel  Heated to high temperature (Partially or fully austenitic): □

    

Hypereutectic steels are partially austenitized to avoid cementite formation on grain boundaries during slow cooling.

Hold for some time and then slow cool. Coarse grain size. Reduced strength. Increased ductility. Homogeneous.

Pearlite

Normalising      

Steel heated just to where austenite is stable. Air cooling – fairly rapid. Grain refinement. Pearlite Stress relief. Higher strength. Higher toughness.

Ferrite

Ferrite

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Recovery and Re-crystallisation  Cold work increases strength and reduces ductility and toughness.  Reversed by recovery and re-crystallisation: □

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Recovery and Recrystallisation Heat treatment temperature (o F)

But if temperature too high excessive grain growth leads to drop in strength and toughness.

 Recovery reduces the stored energy in coldworked or deformed (rolled) material.  Dislocations move and align at heat treatment temperature (recovery).  New defect-free grains nucleate from grain boundaries and grow (recrystallisation). Heat treatment temperature (o C)

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7‐2

Non Equilibrium Heat Treatment - Quenching

Non Equilibrium Heat Treatment - Quenching  Heating to annealing heat treatment temperature range.  Fast cooling to increase hardness:

oC

Austenite

□

Acm

910

□

A3

Annealing

□

727

0.83

0.05

Increased quench severity

 Ductility and toughness are drastically reduced.  Usually followed by tempering.

A1

2.0

Carbon content in weight %

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Tempering

Tempering

 Subcritical (Below A1) Heat treatment to tailor hardness/strength of martensite.  Performed after quenching to reduce the brittleness.  Ductility and toughness are improved.  Removes stresses due to quenching. Hardness

0.008

Brine (Water and salt). Water. Oil.

As- 100 quenched

200

300

400

500

600

700

o

Low C steel (0.12C) Annealed at 900°C for 30 minutes and water quenched. 380Hv

C

After tempering at 700°C for 30 minutes and air cooled. 245Hv

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Heat Treatments Following Welding Stress relief  Carried out at lower temperature, to reduce residual stresses.

Stress Relief and PWHT oC

Austenite 910

Tempering  Carried out at higher temperature (for constructional steels).  Not only relieves stresses but also softens the hard HAZ microstructure.

A3

A1

727

Tempering

600 500

Stress Relief 0.022

0.77 Carbon content in weight %

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Acm

2.0

 No phase transformation.  Slow heating and cooling (max: 50°C/h).  Soaking time 1hr/25mm of thickest section.  Usual temperature for PWHT (C-Mn steel) – 550 to 650°C.  Stress Relief carried out after cold work or welding, at lower temperatures. Copyright © TWI Ltd

7‐3

PWHT Effect on Residual Stress YS at room temperature

Soaking temperature

PWHT Effects

PWHT temperature

Residual stress level

YS at soaking temperature Actual YS Time

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PWHT Recommendations  Provide adequate support (low YS at high temperature!).  Control heating rate to avoid uneven thermal expansions.  Control soak time to equalise temperatures.  Control temperature gradients - No direct flame impingement.  Control furnace atmosphere to reduce scaling.  Control cooling rate to avoid new residual stresses.  For specific PWHT applications see standards, eg ASME VIII, ASME B31.3, ASME B31.8. Copyright © TWI Ltd

Question 1 While inspecting some cast duplex valve bodies one of your inspectors asks if the castings require a heat treatment process. Which of the following would most likely be applied to these items? a. b. c. d.

Solution annealing Quench hardening No heat treatment required Stress relieving would be required but only after welding if applicable

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Heat Treatments You are assigned to a heat treatment company to witness heat treatments being conducted. The heat treatments are being conducted on various products for a major offshore oil and gas project that you have been involved with.

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Question 2 A set of fabricated brackets manufactured from 316L stainless steel is about to be heat-treated, which of the following applies? a. This material is always stressed relieved after welding b. A post weld heat treat isn’t generally conducted on this type of material c. Quench hardening would always be applied to this material to increase toughness after welding d. All options are incorrect Copyright © TWI Ltd

7‐4

Question 3 During the post weld heat treatment of a small welded fabrication, you observe the heat treatment personnel applying heat by a heating torch. In accordance with TWI Specification do you consider this an acceptable practice? a. Yes this is acceptable providing the temperature attained and the soaking times are correct in accordance with the approved PWHT procedure b. Yes this is acceptable providing the thermocouples are correctly placed and calibrated c. No, this application method isn’t acceptable d. 2 options are correct Copyright © TWI Ltd

Question 5 It is a requirement for a quenched and tempered component to undergo post weld heat treatment, one of your inspectors asks you what is the maximum temperature required for this material. Which of the following is correct in accordance the TWI Specification? a. The same as for C/Mn steel b. You would never permit a PWHT to be carried out on this material c. The TWI Specification doesn’t reference this information, but would expect it to be around 680°C d. All options are incorrect Copyright © TWI Ltd

Question 7 After a PWHT process has been carried out on some thick to thin C/Mn pipe spools (12.5mm to 25mm WT) you notice that the heating rate is recorded at 200°C/Hr. In accordance with the TWI Specification is this correct? a. b. c. d.

No, it should be a minimum of 220°C/hr No, it should be 40°C/hr Yes, Providing the cooling rate is the same Yes, providing the cooling rate is 220°C/hr

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Question 4 Unfortunately the stress relieving of a welded fabricated steel structure hasn’t been witnessed by any of your inspectors. When you review the PWHT chart you notice only 2 thermocouples have been used. In accordance with the TWI Specification do you consider this to be acceptable? a. No, all PWHT shall be witnessed and a minimum of 3 thermocouples shall be used b. Yes, only the PWHT charts require reviewing by inspectors c. No, all PWHT shall be witnessed, an inspector has to be present 100% of the time throughout the PWHT process d. No, a minimum of 3 thermocouples shall be used, and calibration certificates require checking prior to the heat treatment process Copyright © TWI Ltd

Question 6 During Post Weld Heat Treatment, what sequence of events occurs to the properties of the material? a. Yield strength increases, stresses decrease then yield strength decreases b. Ductility decreases, stresses increase then ductility increases c. Yield strength decreases, stresses decrease then yield strength increases d. Stresses increase, stresses decrease then yield increases Copyright © TWI Ltd

Question 8 While reviewing the heat treatment chart for a PWHT process you notice that the temperature is not recorded below 150°C on the cooling cycle. Would you accept this chart? a. No, the temperature must be recorded down to room temperature b. It would depend on the thickness and grade of material as to whether this would be acceptable or not c. No, the temperature has to be recorded to at least 110°C d. The TWI Specification doesn’t reference this information. Copyright © TWI Ltd

7‐5

Question 9 In certain cases heat treatments are conducted on cold work components such as cold rolled, steel plate. Which of the following heat treatments would you expect to be conducted on these components? a. b. c. d.

Stress relieving Densensitization Quench hardening Post hydrogen release

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Question 10 You notice from your records you don’t have an inspection report for a component that has undergone a PWHT. In this case what would your course of action be? a. It would be acceptable, If the component had a full inspection report before PWHT b. The TWI Specification makes no reference of this, so you would have to seek advice c. It is a requirement that all components undergo full inspection after a PWHT process has been conducted; in this case it would not be acceptable d. As long as no welding has be conducted after the PWHT process, this would be acceptable Copyright © TWI Ltd

7‐6

Section 8 WPS and Welder Qualifications

8

WPS and Welder Qualifications When structures and pressurised items are fabricated by welding, it is essential that all the welded joints are sound and have suitable properties for their application. Control of welding is by means of welding procedure specifications (WPS) that give detailed written instructions about the welding conditions that must be used to ensure that welded joints have the required properties. Although WPS are shop floor documents to instruct welders, welding inspectors need to be familiar with them because they will need to refer to WPSs when they are checking that welders are working in accordance with the specified requirements. Welders need to understand WPSs and have the skill to make welds that are not defective and demonstrate these abilities before being allowed to make production welds.

8.1

Qualified welding procedure specifications It is industry practice to use qualified WPS for most applications. A welding procedure is usually qualified by making a test weld to demonstrate that the properties of the joint satisfy the requirements specified by the application standard (and the client/end user). Demonstrating the mechanical properties of the joint is the principal purpose of qualification tests but showing that a defect-free weld can be produced is also very important. Production welds that are made in accordance with welding conditions similar to those used for a test weld should have similar properties and therefore be fit for their intended purpose. Figure 8.1 is an example of a typical WPS written in accordance with the European Welding Standard format giving details of all the welding conditions that need to be specified.

8.1.1

Welding standards for procedure qualification European and American Standards have been developed to give comprehensive details about:    

How a welded test piece must be made to demonstrate joint properties. How the test piece must be tested. What welding details need to be included in a WPS? The range of production welding allowed by a particular qualification test weld.

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The principal European Standards that specify these requirements are: BS EN ISO 15614 Specification and qualification of welding procedures for metallic materials – Welding procedure test. Part 1: Arc & gas welding of steels & arc welding of nickel & nickel alloys. Part 2: Arc welding of aluminium and its alloys. The principal American Standards for procedure qualification are: ASME Section IX for pressurised systems (vessels & pipework). AWS D1.1 Structural welding of steels. AWS D1.2 Structural welding of aluminium. 8.1.2

The qualification process for welding procedures Although qualified WPS are usually based on test welds that have been made to demonstrate weld joint properties; welding standards also allow qualified WPS to be written based on other data (for some applications). Some alternative ways that can be used for writing qualified WPS for some applications are:  

Qualification by adoption of a standard welding procedure - test welds previously qualified and documented by other manufacturers. Qualification based on previous welding experience - weld joints that have been repeatedly made and proved to have suitable properties by their service record.

Procedure qualification to European Standards by means of a test weld (and similar in ASME Section IX and AWS) requires a sequence of actions that is typified by those shown by Table 8.1. A successful procedure qualification test is completed by the production of a welding procedure qualification record (WPQR), an example of which is shown by Figure 8.2. 8.1.3

Relationship between a WPQR and a WPS Once a WPQR has been produced, the welding engineer is able to write qualified WPSs for the various production weld joints that need to be made. The welding conditions that are allowed to be written on a qualified WPS are referred to as the qualification range and this range depends on the welding conditions that were used for the test piece (the as-run details) and form part of the WPQR. Welding conditions are referred to as welding variables by European and American Welding Standards and are classified as either essential variables or non-essential variables.

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These variables can be defined as follows: 



Essential variable a variable that has an effect on the mechanical properties of the weldment (and if changed beyond the limits specified by the standard will require the WPS to be re-qualified). Non-essential variable a variable that must be specified on a WPS but does not have a significant effect on the mechanical properties of the weldment (and can be changed without need for re-qualification but will require a new WPS to be written).

It is because essential variables can have a significant effect on mechanical properties that they are the controlling variables that govern the qualification range and determine what can be written into a WPS. If a welder makes a production weld using conditions outside the qualification range given on a particular WPS, there is danger that the welded joint will not have the required properties and there are then two options: 



Make another test weld using similar welding conditions to those used for the affected weld and subject this to the same tests used for the relevant WPQR to demonstrate that the properties still satisfy specified requirements. Remove the affected weld and re-weld the joint strictly in accordance with the designated WPS.

Most of the welding variables that are classed as essential are the same in both the European and American Welding Standards but their qualification ranges may differ. Some Application Standards specify their own essential variables and it is necessary to ensure that these are taken into consideration when procedures are qualified and WPSs are written. Examples of essential variables (according to European Welding Standards) are given in Table 8.2. 8.2

Welder qualification The use of qualified WPSs is the accepted method for controlling production welding but this will only be successful if the welders have the ability to understand and work in accordance with them. Welders also need to have the skill to consistently produce sound welds (free from defects). Welding Standards have been developed to give guidance on what particular test welds are required in order to show that welders have the required skills to make particular types of production welds in particular materials.

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8.2.1

Welding standards for welder qualification The principal European Standards that specify requirements are: EN 287-1 / BS EN ISO 9606

Qualification test of welders – Fusion welding Part 1: Steels

BS EN ISO 9606-2 Qualification test of welders – Fusion welding Part 2: Aluminium and aluminium alloys BS EN ISO 14732

Welding personnel. Qualification testing of welding operators and weld setters for mechanized and automatic welding of metallic materials

The principal American Standards that specify requirements for welder qualification are:

8.2.2

ASME Section IX

Pressurised systems (vessels & pipework)

AWS D1.1

Structural welding of steels

AWS D1.2

Structural welding of aluminium

The qualification process for welders Qualification testing of welders to European Standards requires test welds to be made and subjected to specified tests to demonstrate that the welder understands the WPS and can produce a sound weld. For manual and semi-automatic welding the emphasis of the tests is to demonstrate ability to manipulate the electrode or welding torch. For mechanised and automatic welding the emphasis is on demonstrating that welding operators have ability to control particular types of welding equipment. American Standards allow welders to demonstrate that they can produce sound welds by subjecting their first production weld to non-destructive testing. Table 8.3 shows the steps required for qualifying welders in accordance with European Standards. Figure 8.5 shows a typical Welder Qualification Certificate in accordance with European Standards.

8.2.3

Welder qualification and production welding allowed The welder is allowed to make production welds within the range of qualification recorded on his welder qualification certificate. The range of qualification is based on the limits specified by the Welding Standard for welder qualification essential variables - defined as: a variable that if changed beyond the limits specified by the Welding Standard may require greater skill than has been demonstrated by the test weld.

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Some welding variables that are classed as essential for welder qualification are the same types as those classified as essential for welding procedure qualification, but the range of qualification may be significantly wider. Some essential variables are specific to welder qualification. Examples of welder qualification essential variables are given in Table 8.4. 8.2.4

Period of validity for a welder qualification certificate A welder’s qualification begins from the date of welding of the test piece. The European Standard allows a qualification certificate to remain valid for a period of two years – provided that:  

8.2.5

The welding co-ordinator, or other responsible person, can confirm that the welder has been working within the initial range of qualification. Working within the initial qualification range is confirmed every six months.

Prolongation of welder qualification A welder’s qualification certificate can be prolonged every two years by an examiner/examining body but before prolongation is allowed certain conditions need to be satisfied:  



Records/evidence are available that can be traced to the welder and the WPS that have been used for production welding. The supporting evidence must relate to volumetric examination of the welder’s production welds (RT or UT) on two welds made during the 6 months prior to the prolongation date. The supporting evidence welds must satisfy the acceptance levels for imperfections specified by the European welding standard and have been made under the same conditions as the original test weld.

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Table 8.1 Typical sequence for welding procedure qualification by means of a test weld.

The welding engineer writes a preliminary Welding Procedure Specification (pWPS) for each test coupon to be welded



A welder makes the test coupon in accordance with the pWPS



A welding inspector records all the welding conditions used to make the test coupon (called the as-run conditions)

An Independent Examiner/ Examining Body/Third Party Inspector may be requested to monitor the procedure qualification

The test coupon is subjected to NDT in accordance with the methods specified by the Standard – visual inspection, MT or PT and RT or UT



The test coupon is destructively tested (tensile, bend, macro tests)



The code/application standard/client may require additional tests such as hardness tests, impact tests or corrosion tests – depending on material and application



A Welding Procedure Qualification Record (WPQR) is prepared by the welding engineer giving details of:

» » » » 

The as-run welding conditions Results of the NDT Results of the destructive tests The welding conditions allowed for production welding

If a Third Party Inspector is involved he will be requested to sign the WPQR as a true record of the test

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Table 8.2 Typical examples of WPS essential variables according to European Welding Standards.

VARIABLE

RANGE for PROCEDURE QUALIFICATION

Welding process

No range – process qualified is process that must be used in production

PWHT

Joints tested after PWHT only qualify as PWHT production joints Joints tested ‘as-welded’ only qualify ‘as-welded’ production joints

Parent type

material

Parent materials of similar composition and mechanical properties are allocated the same Material Group No.; qualification only allows production welding of materials with the same Group No.

Welding consumables

Consumables for production welding must have the same European designation – as a general rule

Material thickness

A thickness range is allowed – below and above the test coupon thickness

Type of current

AC only qualifies for AC; DC polarity (+VE or -VE) cannot be changed; pulsed current only qualifies for pulsed current production welding

Preheat temperature

The preheat temperature used for the test is the minimum that must be applied

Interpass temperature

The highest interpass temperature reached in the test is the maximum allowed

Heat input (HI)

When impact requirements apply maximum HI allowed is 25% above test HI when hardness requirements apply minimum HI allowed is 25% below test HI

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Table 8.3 Stages for qualification of a welder.

The welding engineer writes a WPS for welder qualification test piece



The welder makes the test weld in accordance with the WPS

A welding inspector monitors the welding to ensure that the welder is working in accordance the WPS An Independent Examiner/Examining Body/Third Party Inspector may be requested to monitor the test



The test coupon is subjected to NDT in accordance with the methods specified by the Standard (visual inspection, MT or PT and RT or UT)



For certain materials, and welding processes, some destructive testing may be required (bends or macros)



A Welder’s Qualification Certificate is prepared showing the welding conditions used for the test piece and the range of qualification allowed by the Standard for production welding



If a Third Party is involved, the Qualification Certificate would be endorsed as a true record of the test

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Table 8.4 Typical examples of welder qualification essential variables according to European Welding Standards.

VARIABLE

RANGE for WELDER QUALIFICATION

Welding process

No range – process qualified is process that a welder can use in production

Type of weld

Butt welds cover any type of joint except branch welds fillet welds only qualify fillets

Parent type

Parent materials of similar composition and mechanical properties are allocated the same Material Group No.; qualification only allows production welding of materials with the same Group No. but the Groups allow much wider composition ranges than the procedure Groups

material

Filler material

Electrodes and filler wires for production welding must be of the same form as the test (solid wire, flux cored, etc); for MMA coating type is essential. The filler wire must fall within the range of the qualification of the filler material.

Material thickness

A thickness range is allowed; for test pieces above 12mm allow ≥ 5mm

Pipe diameter

Essential and very restricted for small diameters; test pieces above 25mm allow ≥ 0.5 x diameter used (min. 25mm)

Welding positions

Position of welding very important; H-L045 allows all positions (except PG)

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Figure 8.1 Example of a welding procedure specification (WPS) to EN 15614 format.

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Figure 8.2 Example of a WPQR document (qualification range) to EN 15614 format.

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Figure 8.3 Example of WPQR document (test weld details) to EN 15614 format.

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Figure 8.4 Example of a WPQR document (details of weld test) to EN 15614 format.

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Figure 8.5 Example of a welder qualification test certificate (WPQ) to EN 287 format.

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Welding Procedure Qualification Question: What is the main reason for carrying out a Welding Procedure Qualification Test? (What is the test trying to show?)

Welding Procedure and Welder Qualification Section 8

* Properties  Mechanical properties are the main interest - always strength but toughness & hardness may be important for some applications.  Test also demonstrates that the weld can be made without defects. Copyright © TWI Ltd

Welding Procedures Purpose of a WPS  To achieve specific properties. □ Mechanical strength, corrosion resistance, composition.

     

Answer: To show that the welded joint has the properties* that satisfy the design requirements (fit for purpose).

To ensure freedom from defects. To enforce QC procedures. To standardise on methods and costs. To control production schedules. To form a record. Application standard or contract requirement.

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Welding Procedure Qualification (according to BS EN ISO 15614) Preliminary Welding Procedure Specification (pWPS) Welding Procedure Qualification Record (WPQR) Welding Procedure Specification (WPS)

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Welding Procedures Object of a welding procedure test  To give maximum confidence that the welds mechanical and metallurgical properties meet the requirements of the applicable code/specification.  Each welding procedure will show a range to which the procedure is approved (extent of approval).  If a customer queries the approval evidence can be supplied to prove its validity.

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Welding Procedures Producing a welding procedure involves  Planning the tasks.  Collecting the data.  Writing a procedure for use of for trial.  Making a test welds.  Evaluating the results.  Approving the procedure.  Preparing the documentation.

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8‐1

Welding Procedure Qualification Preliminary Welding Procedure Specification (pWPS)

Welding Engineer writes a preliminary Welding Procedure Specification (pWPS) for each test weld to be made.

Welding Procedure Qualification Welding Procedure Qualification Record (WPQR)  A welder makes a test weld in accordance with the pWPS.  A welding inspector records all the welding conditions used for the test weld (referred to as the 'as-run' conditions). An Independent Examiner/ Examining Body/ Third Party inspector may be requested to monitor the qualification process. The finished test weld is subjected to NDT in accordance with the methods specified by the EN ISO Standard - Visual, MT or PT & RT or UT.

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Welding Procedure Qualification Welding Procedure Qualification Record (WPQR)  Test weld is subjected to destructive testing (tensile, bend, macro).  The Application Standard, or Client, may require additional tests such as impact tests, hardness tests (and for some materials - corrosion tests). Welding Procedure Qualification Record (WPQR)  The welding conditions used for the test weld  Results of the NDT.  Results of the destructive tests.  The welding conditions that the test weld allows for production welding.  The Third Party may be requested to sign the WPQR as a true record.

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Welding Procedure Qualification Welding Procedure Specification (WPS)  The welding engineer writes qualified Welding Procedure Specifications (WPS) for production welding.  Production welding conditions must remain within the range of qualification allowed by the WPQR.

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Welding Procedure Qualification

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Welding Procedure Qualification

(according to EN Standards) Welding conditions are called welding variables.

(according to EN Standards) Welding essential variables

Welding variables are classified by the EN ISO Standard as:

Question: Why are some welding variables classified as essential?

 Essential variables.  Non-essential variables.  Additional variables. Note: Additional variables = ASME supplementary essential. The range of qualification for production welding is based on the limits that the EN ISO Standard specifies for essential variables*

Answer: A variable, that if changed beyond certain limits (specified by the Welding Standard) may have a significant effect on the properties* of the joint. * particularly joint strength and ductility.

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8‐2

Welding Procedure Qualification (according to EN Standards) Welding additional variables Question: Why are some welding variables classified as additional? Answer: A variable, that if changed beyond certain limits (specified by the Welding Standard) may have a significant effect on the toughness and/or hardness of the joint. Note: ASME calls variables that affect toughness as supplementary essential variables (but does not refer to hardness).

Welding Procedure Qualification (according to EN Standards) Some typical essential variables  Welding process.  Post weld heat treatment (PWHT).  Material type.  Electrode type, filler wire type (Classification).  Material thickness.  Polarity (AC, DC+ve/DC-ve).  Pre-heat temperature. Some typical additional variables  Heat input.  Welding position.

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Welding Procedures In most codes reference is made to how the procedure are to be devised and whether approval of these procedures is required. The approach used for procedure approval depends on the code. Example codes  AWS D.1.1: Structural Steel Welding Code.  BS 2633: Class 1 welding of Steel Pipe Work.  API 1104: Welding of Pipelines.  BS 4515: Welding of Pipelines over 7 Bar. Other codes may not specifically deal with the requirement of a procedure but may contain information that may be used in writing a weld procedure.  EN 1011: Process of Arc Welding Steels. Copyright © TWI Ltd

Welding Procedures

Welding Procedures Components of a welding procedure Parent material  Type (Grouping).  Thickness.  Diameter (Pipes).  Surface condition. Welding process  Type of process (MMA, MAG, TIG, SAW etc).  Equipment parameters.  Amps, volts, travel speed. Welding consumables  Type of consumable/diameter of consumable.  Brand/classification.  Heat treatments/storage. Copyright © TWI Ltd

Welding Procedures Example Welding Procedure Specification (WPS)

Components of a welding procedure Joint design  Edge preparation.  Root gap, root face.  Jigging and tacking.  Type of backing Welding position  Location, shop or site.  Welding position e.g. PA, PB, PC etc.  Any weather precaution. Thermal heat treatments  Preheat, temps.  Post weld heat treatments eg stress relieving.

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8‐3

Welding Positions PA

1G / 1F

Flat / Downhand Horizontal-Vertical

PB

2F

PC

2G

Horizontal

PD

4F

Horizontal-Vertical (Overhead)

PE

4G

Overhead

PF

3G / 5G

Vertical-Up

PG

3G / 5G

Vertical-Down

H-L045

6G

Inclined Pipe (Upwards)

J-L045

6G

Inclined Pipe (Downwards)

Welding Positions

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Welding Procedures Monitoring heat input As Required by BS EN ISO 15614-1:2004 In accordance with BS EN 1011-1:1998

Welding Procedures 15614-1-2-3

 When impact requirements apply, the upper limit of heat input qualified is 25% greater than that used in welding the test piece.  When hardness requirements apply, the lower limit of heat input qualified is 25% lower than that used in welding the test piece.  Heat input is calculated in accordance with BS EN10111.  If welding procedure tests have been preformed at both a high and low heat input level, then all intermediate heat inputs are also qualified.

Specifies contents of WPS "Shall give details of how a welding operation is to be performed and contain all relevant information". Definitions  Processes to be designated in accordance with BS EN ISO 4063.  Welding positions in accordance with BS EN ISO 6947.  Typical WPS form.

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Welding Procedures BS EN ISO 15614-1:2004 (Replaced BS EN 288-3) "does not invalidate previous … approvals made to former national standards… providing the intent of the technical requirements is satisfied… approvals are relevant" "where additional tests… make the approval technically equivalent… only necessary to do the additional tests…" "approval is valid… in workshops or sites under the same technical and quality control of that manufacturer…" "service, material or manufacturing conditions may require more comprehensive testing… " Application standard may require more testing Copyright © TWI Ltd

Welding Procedures Table 5 Thickness of test piece t

BS EN ISO 15614-1:2004 Range of qualification Single run

Multi run

t1mm, but is mainly used for positional welding of steels >6mm.

Figure 16.10 Pulsed welding waveform and parameters.

4

Globular transfer:

Key characteristics:      

Irregular metal transfer. Medium heat input. Medium deposition rate. Risk of spatter. Not widely used in the UK; can be used for mechanised welding of medium. Thickness steels (typically 3-6mm) in the flat (PA) position.

The globular transfer range occupies the transitional range of arc voltage between free flight and fully short-circuiting transfer. Irregular droplet transfer and arc instability are inherent, particularly when operating near the transition threshold. In globular transfer, a molten droplet of several times the electrode diameter forms on the wire tip. Gravity eventually detaches the globule when its weight overcomes surface tension forces and transfer takes place often with excessive spatter To minimise spatter levels, it is common to operate with a very short arc length and in some cases a buried arc technique is adopted. Globular transfer can only be used in the flat position and is often associated with lack of penetration, fusion defects and uneven weld beads, because of the irregular transfer and tendency for arc wander.

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16.2.8 Inductance What does inductance do? When MIG welding in the dip transfer mode, the welding electrode touches the weld pool, causing a short circuit. During the short circuit, the arc voltage is nearly zero. If the constant voltage power supply responded instantly, very high current would immediately begin to flow through the weldingcircuit. The rapid rise in current to a high value would melt the short-circuited electrode free with explosive force, dispelling the weld metal and causing considerable spatter. Inductance is the property in an electrical circuit that slows down the rate of current rise (Figure 16.11). The current travelling through an inductance coil creates a magnetic field. This magnetic field creates a current in the welding circuit that is in opposition to the welding current. Increasing the inductance will also increase the arc time and decrease the frequency of short-circuiting. For each electrode feed rate, there is an optimum value of inductance. Too little inductance results in excessive spatter. If too much inductance is used, the current will not rise fast enough and the molten tip of the electrode is not heated sufficiently causing the electrode to stub into the base metal. Modern electronic power sources automatically set the inductance to give a smooth arc and metal transfer.

Figure 16.11 Relationship between inductance and current rise.

16.3

Welding consumables

16.3.1 Solid wires Usually made in sizes from 0.6 to 1,6mm diameter they are produced with an analysis which essentially matches the materials being joined. Additional elements are often added especially extra de-oxidants in steel wires. C-Mn and low alloy steel wires are usually copper coated to reduce the risk of rusting and promote better electrical contact.

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16.3.2 Flux cored wires A cored wire consists of a metal sheath containing a granular flux. This flux can contain elements that would normally be used in MMA electrodes and so the process has a very wide range of applications. In addition we can also add gas producing elements and compounds to the flux and so the process can become independent of a separate gas shield, which restricted the use of conventional MIG/MAG welding in many field applications. Most wires are sealed mechanically and hermetically with various forms of joint. The effectiveness of the joint of the wire is an inspection point of cored wire welding as moisture can easily be absorbed into a damaged or poor seam. Wire types commonly used are:    

Rutile – which give good positional capabilities.. Basic – also positional but good on “dirty” material. Metal cored – higher productivity and some having excellent root run capabilities. Self-shielded – no external gas needed.

Baking of cored wires is ineffective and will do nothing to restore the condition of a contaminated flux within a wire. Note: Unlike MMA electrodes the potential hydrogen levels and mechanical properties of welds with rutile wires can equal those of the basic types. 16.4

Important inspection points/checks when MIG/MAG welding 1

The welding equipment A visual check should be made to ensure the welding equipment is in good condition.

2

The electrode wire The diameter, specification and the quality of the wire are the main inspection headings. The level of de-oxidation of the wire is an important factor with single, double and triple de-oxidised wires being available. The higher the level of de-oxidants in the wire, then the lower the chance of porosity in the weld. The quality of the wire winding, copper coating, and temper are also important factors in minimising wire feed problems. Quality of wire windings and increasing costs

(a) Random wound. (b) Layer wound. (c) Precision layer wound. 3

The drive rolls and liner. Check the drive rolls are of the correct size for the wire and that the pressure is only hand tight, or just sufficient to drive the wire. Any excess pressure will deform the wire to an ovular shape. This will make the wire very difficult to drive through the liner and result in arcing in the contact tip and excessive wear of the contact tip and liner. Check that the liner is the correct type and size for the wire. A size of liner will generally fit 2 sizes of wire ie (0.6 and 0.8) (1.0 and 1.2) (1.4 and 1.6) mm diameter. Steel liners are used for steel wires and Teflon liners for aluminium wires.

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The contact tip Check that the contact tip is the correct size for the wire being driven, and check the amount of wear frequently. Any loss of contact between the wire and contact tip will reduce the efficiency of current pick. Most steel wires are copper-coated to maximise the transfer of current by contact between 2 copper surfaces at the contact tip, this also inhibits corrosion. The contact tip should be replaced regularly.

5

The connections The length of the electric arc in MIG/MAG welding is controlled by the voltage settings. This is achieved by using a constant voltage volt/amp characteristic inside the equipment. Any poor connection in the welding circuit will affect the nature and stability of the electric arc, and is thus is a major inspection point.

6

Gas and gas flow rate The type of gas used is extremely important to MIG/MAG welding, as is the flow rate from the cylinder, which must be adequate to give good coverage over the solidifying and molten metal to avoid oxidation and porosity.

7

Other variable welding parameters Checks should be made for correct wire feed speed, voltage, speed of travel, and all other essential variables of the process given on the approved welding procedure.

8

Safety checks Checks should be made on the current carrying capacity, or duty cycle of equipment and electrical insulation. Correct extraction systems should be in use to avoid exposure to ozone and fumes.

A check should always be made to ensure that the welder is qualified to weld the procedure being employed. Typical welding imperfections: 1 2 3 4

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Silica inclusions, (on ferritic steels only) caused by poor inter-run cleaning. Lack of sidewall fusion during dip transfer welding thick section vertically down. Porosity caused from loss of gas shield and low tolerance to contaminants. Burn-through from using the incorrect metal transfer mode on sheet metal.

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Section 17 MMA Welding

17

MMA Welding

17.1

Manual metal arc/shielded metal arc welding (MMA/SMAW) The most versatile of the welding processes, manual metal arc (MMA) welding is suitable for welding most ferrous and non-ferrous metals, over a wide range of thicknesses. The MMA welding process can be used in all positions, with reasonable ease of use and relatively economically. The final weld quality is primarily dependent on the skill of the welder. When an arc is struck between the coated electrode and the workpiece, both the electrode and workpiece surface melt to form a weld pool. The average temperature of the arc is approximately 6000°C, which is sufficient to simultaneously melt the parent metal, consumable core wire and the flux coating. The flux forms gas and slag, which protects the weld pool from oxygen and nitrogen in the surrounding atmosphere. The molten slag solidifies and cools and must be chipped off the weld bead once the weld run is complete (or before the next weld pass is deposited). The process allows only short lengths of weld to be produced before a new electrode needs to be inserted in the holder.

Figure 17.1 The manual metal arc welding process.

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17.2

MMA welding basic equipment requirements 10

1

9

2

3

8

4

7

5

6 1 2 3 4 5 6 7 8 9 10

Power source transformer/rectifier (constant current type). Holding oven (holds at temperatures up to 150°C). Inverter power source (more compact and portable). Electrode holder (of a suitable amperage rating). Power cable (of a suitable amperage rating). Welding visor (with correct rating for the amperage/process). Power return cable (of a suitable amperage rating). Electrodes (of a suitable type and amperage rating). Electrode oven (bakes electrodes at up to 350°C). Control panel (on\off/amperage/polarity/OCV).

Figure 17.2 MMA welding basic equipment.

17.3

Power requirements Manual metal arc welding can be carried out using either direct (DC) or alternating (AC) current. With DC welding current either positive (+ve) or negative (-ve) polarity can be used, so current is flowing in one direction. AC welding current flows from negative to positive and is two directional. Power sources for MMA welding are transformers (which transforms mains AC to AC suitable for welding), transformer-rectifiers (which rectifies AC to DC), diesel or petrol driven generators (preferred for site work) or inverters (a more recent addition to welding power sources). For MMA welding a power source with a constant current (drooping) output characteristic must be used.

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The power source must provide:     

17.4

An open circuit voltage (OCV) to initiate the arc, between 50 and 90V. Welding voltage to maintain the arc during welding, between 20 and 30V. A suitable current range, typically 30-350A. A stable arc. Rapid arc recovery or arc re-ignition without current surge. A constant welding current. The arc length may change during welding, but consistent electrode burn-off rate and weld penetration characteristics must be maintained during welding.

Welding variables Other factors, or welding variables, which affect the final quality of the MMA weld, are:     

Current (amperage) Voltage. Travel speed. Polarity. Type of electrode.

affects heat Input

17.4.1 Current (amperage) Amperage controls burn-off rate and depth of penetration. Welding current level is determined by the size of electrode and the welding position - manufacturers recommend the normal operating range and current. Incorrect amperage settings when using MMA can contribute to the following: Amperage too low Poor fusion or penetration, irregular weld bead shape, slag inclusion unstable arc, porosity, potential arc strikes, difficult starting. Amperage too high Excessive penetration, burn-through, undercut, spatter, porosity, deep craters, electrode damage due to overheating, high deposition making positional welding difficult. 17.5

Voltage Open circuit voltage (OCV) is the voltage measured between the output terminals of the power source when no current is flowing through the welding circuit. For safety reasons this should not exceed 100V and is usually between 50-90V. Arc voltage is the voltage required to maintain the arc during welding and is usually between 20–30V. As arc voltage is a function of arc length the welder controls the arc length and therefore the arc voltage. Arc voltage controls weld pool fluidity.

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The effects of having the wrong arc voltage can be: Arc Voltage too low Poor penetration, electrode stubbing, lack of fusion defects, potential for arc strikes, slag inclusion, unstable arc condition, irregular weld bead shape. Arc voltage too high Excessive spatter, porosity, arc wander, irregular weld bead shape, slag inclusions, fluid weld pool making positional welding difficult. 17.5.1 Travel speed Travel speed is related to whether the welding is progressed by stringer beads or by weaving. Often the run out length (ROL) ie the length of deposit from one standard electrode is quoted on procedures rather than speed as it is easier for the welder to visualise. Travel speed too fast Narrow thin weld fusion/penetration.

bead,

fast

cooling,

slag

inclusions,

undercut,

poor

Travel speed too slow Cold lap, excess weld deposition, irregular bead shape, undercut. 17.6

Type of current and polarity Polarity will determine the distribution of heat energy at the welding arc. The preferred polarity of the MMA system depends primarily upon the electrode being used and the desired properties of the weld. 

Direct current. electrode positive (DCEP / DC+). Usually produces the greatest penetration but with lesser deposition rate. Known in some standards as reverse polarity.



Direct current. electrode negative (DCEN / DC-) Usually produces less penetration with greater deposition rate. Known in some standards as straight polarity.

When using direct current the arc can be affected by arc blow. The deflection of the arc from its normal path due to magnetic forces. 

Alternating current (AC) The distribution of heat energy at the arc is equal.



Operating factor (O/F) The percentage (%) of arc on time in a given time span.

When compared with semi automatic welding processes the MMA welding process has a low O/F of approximately 30% Manual semi-automatic MIG/MAG O/F is in the region 60% with fully automated MIG/MAG in the region of 90% O/F. A welding process O/F can be directly linked to productivity. Operating Factor should not to be confused with the term duty cycle, which is a safety value given as the % of time a conductor can carry a current and is given as a specific current at 60 and 100% of 10 minutes ie 350A 60% and 300A 100%.

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17.7

Type of consumable electrode For MMA welding there are three generic types of flux covering: Rutile, basic, cellulosic The details of these types are covered elsewhere in these notes.

17.8

Typical welding defects 1

Slag inclusions caused by poor welding technique or insufficient inter-run cleaning.

2

Porosity from using damp or damaged electrodes or when welding contaminated or unclean material.

3

Lack of root fusion or penetration caused by in-correct settings of the amps, root gap or face width.

4

Undercut caused by too high amperage for the position or by a poor welding technique eg travel speed too fast or too slow, arc length (therefore voltage) variations particularly during excessive weaving.

5

Arc strikes caused by incorrect arc striking procedure, or lack of skill. These may be also caused by incorrectly fitted/secured power return lead clamps.

6

Hydrogen cracks caused by the use of incorrect electrode type or incorrect baking procedure and/or control of basic coated electrodes.

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Section 18 Submerged Arc Welding

18

Submerged Arc Welding

18.1

The process Abbreviated as SAW, this is a welding process where an arc is struck between a continuous bare wire and the parent plate. The arc, electrode end and the molten pool are submerged in an agglomerated or fused powdered flux, which turns, into gas and slag in its lower layers when subjected to the heat of the arc, thus protecting the weld from contamination. The wire electrode is fed continuously by a feed unit of motor-driven rollers, which usually are voltage-controlled to ensure an arc of constant length. The flux is fed from a hopper fixed to the welding head, and a tube from the hopper spreads the flux in a continuous elongated mound in front of the arc along the line of the intended weld and of sufficient depth to submerge the arc completely so that there is no spatter, the weld is shielded from the atmosphere and there are no ultraviolet or infra-red radiation effects (see below). Unmelted flux is reclaimed for use. The use of powdered flux restricts the process to the flat and horizontal-vertical welding positions.

Submerged arc welding is noted for its ability to employ high weld currents owing to the properties and functions of the flux. Such currents give deep penetration and high deposition rates. Generally a DC electrode positive polarity is employed up to about 1000A because it produces a deep penetration. On some applications (ie cladding operations) DC electrode negative is needed to reduce penetration and dilution. At higher currents or in case of multiple electrode systems, AC is often preferred to avoid the problem of arc blow (when used with multiple electrode systems, DC electrode positive is used for the lead arc and AC is used for the trail arc).

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Power sources can be of the constant current or constant voltage type either may have outputs exceeding 1000A.

Difficulties sometimes arise in ensuring conformity of the weld with a predetermined line owing to the obscuring effect of the flux. Where possible, a guide wheel or stylus to run in the joint preparation is positioned in front of the welding head and flux hoppers or alternatively a laser tracking system is used. Submerged arc welding is widely used in the fabrication of ships, pressure vessels, linepipe, railway carriages and anywhere where long welds are required. It can be used to weld thicknesses from 1.5mm upwards. Materials joined     

18.2

Welding of carbon steels. Welding low alloy steels (eg fine grained and creep resisting). Welding stainless steels. Welding nickel alloys. Cladding to base metals to improve wear and corrosion resistance.

Process variables There are several variables which when changed can have an effect on the weld appearance and mechanical properties:           

Welding current. Type of flux and particle distribution. Arc voltage. Travel speed. Electrode size. Electrode extension. Type of electrode. Width and depth of the layer of flux. Electrode angle, (leading, trailing). Polarity. Single-, double- or multi-wire system.

18.2.1 Welding current Welding current effect on weld profile (2.4mm electrode diameter, 35V arc voltage and 610mm/min travel speed) 



Excessively high current produces a deep penetrating arc with a tendency to burn-through, undercut or a high, narrow bead prone to solidification cracking. Excessively low current produces an unstable arc, lack of penetration and possibly lack of fusion.

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350A

500A

650A

18.2.2 Arc voltage Arc voltage adjustment varies the length of the arc between the electrode and the molten weld metal. If the arc voltage increases, the arc length increases and vice versa. The voltage principally determines the shape of the weld bead cross section and its external appearance.

25V

35V

45V

Arc voltage effect on weld profile (2.4mm electrode diameter, 500A welding current and 610mm/min travel speed). Increasing the arc voltage will:     

Produce a flatter and wider bead. Increase flux consumption. Tend to reduce porosity caused by rust or scale on steel. Help to bridge excessive root opening when fit-up is poor. Increase pick-up of alloying elements from the flux when they are present.

Excessively high arc voltage will:     

Produce a wide bead shape that is subject to solidification cracking. Make slag removal difficult in groove welds. Produce a concave shaped fillet weld that may be subject to cracking. Increase undercut along the edge(s) of fillet welds. Over-alloy the weld metal, via the flux.

Reducing the arc voltage with constant current and travel speed will: 

Produce a stiffer arc which improves penetration in a deep weld groove and resists arc blow.

Excessively low arc voltage will:  

Produce a high, narrow bead. Causes difficult slag removal along the weld toes.

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18.2.3 Travel speed If the travel speed is increased:   

Heat input per unit length of weld is decreased. Less filler metal is applied per unit length of weld, and consequently less excess weld metal. Penetration decreases and thus the weld bead becomes smaller.

300mm/min

610mm/min

1220mm/min

Travel speed effect on weld profile (2.4mm electrode diameter, 500A welding current and 35V arc voltage). 18.2.4 Electrode size Electrode size affects: 



The weld bead shape and the depth of penetration at a given current: a high current density results in a stiff arc that penetrates into the base metal. Conversely, a lower current density in the same size electrode results in a soft arc that is less penetrating. The deposition rate: at any given amperage setting, a small diameter electrode will have a higher current density and a higher deposition rate of molten metal than a larger diameter electrode. However, a larger diameter electrode can carry more current than a smaller electrode, so the larger electrode can ultimately produce a higher deposition rate at higher amperage.

3.2 mm

4.0 mm

5.0 mm

Electrode size effect on weld profile (600A welding current, 30V arc voltage and 760mm/min travel speed).

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18.2.5 Electrode extension The electrode extension is the distance the continuous electrode protrudes beyond the contact tip. At high current densities, resistance heating of the electrode between the contact tip and the arc can be utilised to increase the electrode melting rate (as much as 25-50%). The longer the extension, the greater the amount of heating and the higher the melting rate (see below).

30mm

45mm

60mm

80mm

18.2.6 Type of electrode An electrode with a low electrical conductivity, such as stainless steel, can with a normal electrode extension experience greater resistance heating. Thus for the same size electrode and current, the melting rate of a stainless steel electrode will be higher than that of a carbon steel electrode. 18.2.7 Width and depth of flux The width and depth of the layer of granular flux influence the appearance and soundness of the finished weld as well as the welding action. If the granular layer is too deep, the arc is too confined and a rough weld with a rope-like appearance is likely to result, it may also produce local flat areas on the surface often referred to as gas flats. The gases generated during welding cannot readily escape, and the surface of the molten weld metal is irregularly distorted. If the granular layer is too shallow, the arc will not be entirely submerged in flux. Flashing and spattering will occur. The weld will have a poor appearance, and it may show porosity. 18.3

Storage and care of consumables Care must be given to fluxes supplied for SAW which, although they may be dry when packaged, may be exposed to high humidity during storage. In such cases they should be stored in accordance with the manufacturer's recommendations before use, or porosity or cracking may result. It rarely practical or economical to re-dry fluxes which may have picked up moisture. Ferrous wire coils supplied as continuous feeding electrodes are usually coppercoated. This provides some corrosion resistance, ensures good electrical contacts and helps in smooth feeding. Rust and mechanical damage should be avoided in such products, as they will both interrupt smooth feeding of the electrode. Rust will be detrimental to weld quality generally since rust is a hygroscopic material (may contain or absorb moisture) and thus it can lead to hydrogen induced cracking. Contamination by carbon containing materials such as oil, grease, paint and drawing lubricants is especially harmful with ferrous metals. Carbon pick-up in the weld metal can cause a marked and usually undesirable change in properties. Such contaminants may also result in hydrogen being absorbed in the weld pool. Welders should always follow the consumables storage and handling.

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manufacturer's

recommendations

for

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Section 19 TIG Welding

19

TIG Welding

19.1

Process characteristics In the USA the TIG process is also called gas tungsten arc welding (GTAW). TIG welding is a process where melting is produced by heating with an arc struck between a non-consumable tungsten electrode and the workpiece. An inert gas is used to shield the electrode and weld zone to prevent oxidation of the tungsten electrode and atmospheric contamination of the weld and hot filler wire (as shown below).

Figure 19.1 Manual TIG welding.

Tungsten is used because it has a melting point of 3370°C, which is well above any other common metal. The power source is of the constant current type. 19.2

Process variables The main variables in TIG welding are:     

Welding current. Current type and polarity. Travel speed. Shape of tungsten electrode tip and vertex angle. Shielding gas flow rate.

Each of these variables is considered in more detail in the following subsections.

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19.2.1 Welding current   

Weld penetration is directly related to welding current. If the welding current is too low, the electrode tip will not be properly heated and an unstable arc may result. If the welding current is set too high, the electrode tip might overheat and melt, leading to tungsten inclusions.

19.2.2 Current type and polarity  





With steels DC electrode negative is used. Materials which have refractory oxides such as those of aluminium or magnesium are welded using AC or DC electrode positive which break up the oxide layer. With a DC positively connected electrode, heat is concentrated at the electrode tip and therefore for DC positive welding the electrode needs to be of greater diameter than when using DC negative if overheating of the tungsten is to be avoided. A water-cooled torch is recommended if DC positive is used. The current carrying capacity of a DC positive electrode is about one tenth that of a negative one and it is therefore limited to welding thin sections.

19.2.3 Travel speed   

Travel speed affects both weld width and penetration but the effect on width is more pronounced than on penetration. Increasing the travel speed reduces the penetration and width. Reducing the travel speed increases the penetration and width.

19.2.4 Tungsten electrode types Different types of tungsten electrodes can be used to suit different applications:  





WIS10-30816 TIG Welding

Pure tungsten electrodes are rarely used. Thoriated electrodes are alloyed with thorium oxide, typically 2%, to improve arc initiation. They have higher current carrying capacity than pure tungsten electrodes and maintain a sharp tip for longer. Unfortunately, thoria is slightly radioactive (emitting α radiation) and the dust generated during tip grinding should not be inhaled. Electrode grinding machines used for thoriated tungsten grinding should be fitted with a dust extraction system. Ceriated and lanthanated electrodes are alloyed with cerium and lanthanum oxides, for the same reason as thoriated electrodes. They operate successfully with DC or AC but since cerium and lanthanum are not radioactive, these types have been used as replacements for thoriated electrodes Zirconiated electrodes are alloyed with zirconium oxide. Operating characteristics of these electrodes fall between the thoriated types and pure tungsten. However, since they are able to retain a balled end during welding, they are recommended for AC welding. Also, they have a high resistance to contamination and so they are used for high integrity welds where tungsten inclusions must be avoided.

19-2

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19.2.5 Shape of tungsten electrode tip 



     

With DC electrode negative, thoriated, ceriated or lanthanated tungsten electrodes are used with the end is ground to a specific angle (the electrode tip angle or vertex angle – shown below). As a general rule, the length of the ground portion of the tip of the electrode should have a length equal to approximately 2-2.5 times the electrode diameter. The tip of the electrode is ground flat to minimise the risk of the tip breaking off when the arc is initiated or during welding (shown below). If the vertex angle is increased, the penetration increases. If the vertex angle is decreased, bead width increases. For AC welding, pure or zirconiated tungsten electrodes are used. These are used with a hemispherical (‘balled’) end (as shown below). In order to produce a balled end the electrode is grounded, an arc initiated and the current increased until it melts the tip of the electrode.

Electrode tip angle (or vertex angle)

Electrode tip with with flat end

Electrode tip with a balled end

Figure 19.2 Examples of shapes of electrode tips.

19.3

Filler wires and shielding gases These are selected on the basis of the materials being welded. See the relevant chapter in these notes.

19.4

Tungsten inclusions Small fragments of tungsten that enter a weld will always show up on radiographs (because of the relatively high density of this metal) and for most applications will not be acceptable. Thermal shock to the tungsten causing small fragments to enter the weld pool is a common cause of tungsten inclusions and is the reason why modern power sources have a current slope-up device to minimise this risk. This device allows the current to rise to the set value over a short period and so the tungsten is heated more slowly and gently.

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19.5

Crater cracking Crater cracking is one form of solidification cracking and some filler metals can be sensitive to it. Modern power sources have a current slope-out device so that at the end of a weld when the welder switches off the current it reduces gradually and the weld pool gets smaller and shallower. This means that the weld pool has a more favourable shape when it finally solidifies and crater cracking can be avoided.

19.6

Common applications of the TIG process These include autogenous welding of longitudinal seams, in thin walled pipes and tubes, in stainless steel and other alloys, on continuous forming mills. Using filler wires, TIG is used for making high quality joints in heavier gauge pipe and tubing for the chemical, petroleum and power generating industries. It is also in the aerospace industry for such items as airframes and rocket motor cases.

19.7

Advantages of the TIG process  

  



19.8

It produces superior quality welds, with very low levels of diffusible hydrogen and so there is less danger of cold cracking. It does not give weld spatter nor slag inclusions which makes it particularly suitable for applications that require a high degree of cleanliness (eg pipework for the food and drinks industry, semi-conductors manufacturing, etc). It can be used with filler metal and on thin sections without filler; it can produce welds at relatively high speed. It enables welding variables to be accurately controlled and is particularly good for controlling weld root penetration in all positions of welding. It can be used to weld almost all weldable metals, including dissimilar joints, but is not generally used for those with low melting points such as lead and tin. The method is especially useful in welding the reactive metals with very stable oxides such as aluminium, magnesium, titanium and zirconium. The heat source and filler metal additions are controlled independently and thus it is very good for joining thin base metals.

Disadvantages of the TIG process      

WIS10-30816 TIG Welding

It gives low deposition rates compared with other arc welding processes. There is a need for higher dexterity and welder co-ordination than with MIG/MAG or MMA welding. It is less economical than MMA or MIG/MAG for sections thicker than ~10mm. It is difficult to fully shield the weld zone in draughty conditions and so may not be suitable for site/field welding. Tungsten inclusions can occur if the electrode is allowed to contact the weld pool. The process does not have any cleaning action and so has low tolerance for contaminants on filler or base metals.

19-4

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Section 20 Welding Repairs

20

Weld Repairs Weld repairs can be divided into two specific areas: 1 2

Production repairs. In service repairs.

The reasons for making a repair are many and varied. Typically, they range from the removal of weld defects induced during manufacture to a quick and temporary running-repair to an item of production plant. In these terms, the subject of welding repairs is also wide and varied and often confused with maintenance and refurbishment where the work can be scheduled. With planned maintenance and refurbishment, sufficient time can be allowed to enable the tasks to be completed without production pressures being applied. In contrast, repairs are usually unplanned and may result in shortcuts being taken to allow the production programme to continue. It is, therefore, advisable for a fabricator to have an established policy on repairs and to have repair methods and procedures in place. The manually controlled welding processes are the easiest to use, particularly if it is a local repair or one to be carried out on-site. Probably the most frequently used of these processes is manual metal arc (MMA) as this is versatile, portable and readily applicable to many alloys because of the wide range of off-the-shelf consumables. Repairs almost always result in higher residual stresses and increased distortion compared with first time welds. With carbon-manganese and low/medium alloy steels, the application of preheat and post-weld heat treatments may be required. There are a number of key factors that need to be considered before undertaking any repair. The most important being a judgement as to whether it is financially worthwhile. Before this judgement can be made, the fabricator needs to answer the following questions: 1 2 3 4 5

Can structural integrity be achieved if the item is repaired? Are there any alternatives to welding? What caused the defect and is it likely to happen again? How is the defect to be removed and what welding process is to be used? Which non-destructive testing (NDT) is required to ensure complete removal of the defect? 6 Will the welding procedures require approval/re-approval? 7 What will be the effect of welding distortion and residual stress? 8 Will heat treatment be required? 9 What NDT is required and how can acceptability of the repair be demonstrated? 10 Will approval of the repair be required - if yes, how and by whom? Although a weld repair may be a relatively straightforward activity, in many instances it can be quite complex and various engineering disciplines may need to be involved to ensure a successful outcome. It is recommended that there be an ongoing analysis of the types of defect carried out by the Q/C department to discover the likely reason for their occurrence, (Material/process or skill related.)

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In general terms, a welding repair involves: 1

A detailed assessment to find out the extremity of the defect. This may involve the use of a surface or sub-surface NDT methods. 2 Cleaning the repair area, (removal of paint grease etc). 3 Once established the excavation site must be clearly identified and marked out. 4 An excavation procedure may be required (method used ie grinding, arc-air gouging, preheat requirements etc). 5 NDT should be used to locate the defect and confirm its removal. 6 A welding repair procedure/method statement with the appropriate* welding process, consumable, technique, controlled heat input and interpass temperatures etc will need to be approved. 7 Use of approved welders. 8 Dressing the weld and final visual. 9 NDT procedure/technique prepared and carried out to ensure that the defect has been successfully removed and repaired. 10 Any post repair heat treatment requirements. 11 Final NDT procedure/technique prepared and carried out after heat treatment requirements. 12 Applying protective treatments (painting etc as required). (*Appropriate’ means suitable for the alloys being repaired and may not apply in specific situations)

20.1

Production repairs Repairs are usually identified during production inspection and evaluation of the reports is usually carried out by the Welding Inspector, or NDT operator. Discontinuities in the welds are only classed as defects when they are outside the permitted range permitted by the applied code or standard. Before the repair can commence, a number of elements need to be fulfilled.

20.1.1 Analysis As this defect is surface breaking and has occurred at the fusion face the problem could be cracking or lack of sidewall fusion. If the defect is found to be cracking the cause may be associated with the material or the welding procedure, however if the defect is lack of sidewall fusion this can be apportioned to the lack of skill of the welder. 20.1.2 Assessment In this particular case as the defect is open to the surface, magnetic particle inspection (MPI) or dye penetrant inspection (DPI) may be used to gauge the length of the defect and ultrasonic testing (U/T) used to gauge the depth.

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A typical defect is shown below:

Plan view of defect

20.1.3 Excavation If a thermal method of excavation is being used ie arc-air gouging it may be a requirement to qualify a procedure as the heat generated may have an affect on the metallurgical structure, resulting in the risk of cracking in the weld or parent material

To prevent cracking it may be necessary to apply a preheat. The depth to width ratio shall not be less than 1 (depth) to 1 (width) ideally 1 to 1.5 would be recommended (ratio: depth 1 to the width 1.5).

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Side view of excavation for slight sub surface defect.

W

D

Side view of excavation for deep defect.

W D

Side view of excavation for full root repair.

W D

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20.1.4 Cleaning of the excavation At this stage grinding of the repair area is important, due to the risk of carbon becoming impregnated into the weld metal/parent material. It should be ground back typically 3-4mm to bright metal.

Confirmation of excavation At this stage NDT should be used to confirm that the defect has been completely excavated from the area.

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20.1.5 Re-welding of the excavation Prior to re-welding of the excavation a detailed repair welding procedure/ method statement shall be approved.

Typical side view of weld repair

20.1.6 NDT confirmation of successful repair After the excavation has been filled the weldment should then undergo a complete retest using the same NDT techniques as previously used to establish the original repair, this is carried out to ensure no further defects have been introduced by the repair welding process. NDT may also need to be further applied after any additional post-weld heat treatment has been carried out. 20.2

In-service repairs Most in-service repairs can be of a very complex nature, as the component is very likely to be in a different welding position and condition than it was during production. It may also have been in contact with toxic or combustible fluids hence a permit to work will need to be sought prior to any work being carried out. The repair welding procedure may look very different to the original production procedure due to changes in these elements. Other factors may also be taken into consideration, such as the effect of heat on any surrounding areas of the component ie electrical components, or materials that may become damaged by the repair procedure. This may also include difficulty in carrying out any required pre- or post-welding heat treatments and a possible restriction of access to the area to be repaired. For large fabrications it is likely that the repair must also take place on-site and without a shut down of operations, which may bring other elements that need to be considered. Repair of in service defects may require consideration of these and many other factors, and as such are generally considered more complicated than production repairs. Joining technologies often play a vital role in the repair and maintenance of structures. Parts can be replaced, worn or corroded parts can be built up, and cracks can be repaired.

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When a repair is required it is important to determine two things: firstly, the reason for failure and, secondly, can the component actually be repaired? The latter point infers that the material type is known. For metals, particularly those to be welded, the chemical composition is vitally important. Failure modes often indicate the approach required to make a sound repair. When the cause-effect analysis, however simple, is not followed through it is often the case that the repair is unsafe - sometimes disastrously so. In many instances, the Standard or Code used to design the structure will define the type of repair that can be carried out and will also give guidance on the methods to be followed. Standards imply that when designing or manufacturing a new product it is important to consider a maintenance regime and repair procedures. Repairs may be required during manufacture and this situation should also be considered. Normally, there is more than one way of making a repair. For example, cracks in cast iron might be held together or repaired by: pinning, bolting, riveting, welding, or brazing. The method chosen will depend on factors such as the reason for the failure, the material composition and cleanliness, the environment and the size and shape of the component. It is very important that repair and maintenance welding are not regarded as activities, which are simple or straightforward. In many instances a repair may seem undemanding but the consequences of getting it wrong can be catastrophic failure with disastrous consequences. Is welding the best method of repair? If repair is called for because a component has a local irregularity or a shallow defect, grinding out any defects and blending to a smooth contour might well be acceptable. It will certainly be preferable if the steel has poor weldability or if fatigue loading is severe. It is often better to reduce the so-called factor of safety slightly, than to risk putting defects, stress concentrations and residual stresses into a brittle material. In fact brittle materials - which can include some steels (particularly in thick sections) as well as cast irons - may not be able to withstand the residual stresses imposed by heavy weld repairs, particularly if defects are not all removed, leaving stress concentrations to initiate cracking. Is the repair really like earlier repairs? Repairs of one sort may have been routine for many years. It is important, however, to check that the next one is not subtly different. For example, the section thickness may be greater; the steel to be repaired may be different and less weldable, or the restraint higher. If there is any doubt, answer the remaining questions. What is the composition and weldability of the base metal? The original drawings will usually give some idea of the steel involved, although the specification limits may then have been less stringent, and the specification may not give enough compositional details to be helpful. If sulphur-bearing free-machining steel is involved, it could give hot cracking problems during welding.

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If there is any doubt about the composition, a chemical analysis should be carried out. It is important to analyse for all elements, which may affect weldability (Ni, Cr, Mo, Cu, V, Nb and B) as well as those usually, specified (C, S, P, Si and Mn). A small cost spent on analysis could prevent a valuable component being ruined by ill-prepared repairs or, save money by reducing or avoiding the need for preheat if the composition were leaner than expected. Once the composition is known, a welding procedure can be devised. What strength is required from the repair? The higher the yield strength of the repair weld metal, the greater will be the residual stress level on completion of welding, the greater the risk of cracking, the greater the clamping needed to avoid distortion and more difficulty in formulating the welding procedure. In any case, the practical limit for the yield strength of conventional steel weld metals is about 1000N/mm2. Can preheat be tolerated? Not only does a high level of preheat make conditions more difficult for the welder; the parent steel can be damaged if it has been tempered at a low temperature. In other cases the steel being repaired may contain items, which are damaged by excessive heating. Preheat levels can be reduced by using consumables of ultra-low hydrogen content or by non-ferritic weld metals. Of these, austenitic electrodes may need some preheat, but the more expensive nickel alloys usually do not. However, the latter may be sensitive to high sulphur and phosphorus contents in the parent steel if diluted into the weld metal. Can softening be tolerated?

or

hardening

of

the

heat

affected

zone

(HAZ)

Softening of the HAZ is likely in very high strength steels, particularly if they have been tempered at low temperatures. Such softening cannot be avoided, but its extent can be minimised. Hard HAZs are particularly vulnerable where service conditions can lead to stress corrosion. Solutions containing H 2 S (hydrogen sulphide) may demand hardness’ below 248HV (22HRC) although fresh aerated seawater appears to tolerate up to about 450HV. Excessively hard HAZ’s may, therefore, require post-weld heat treatment (PWHT) to soften them but provided cracking has been avoided. Is PWHT practicable? Although it may be desirable, PWHT may not be possible for the same reasons that preheating is not possible. For large structures, local PWHT may be possible, but care should be taken to abide by the relevant codes, because it is all too easy to introduce new residual stresses by improperly executed PWHT. Is PWHT necessary? PWHT may be needed for one of several reasons, and the reason must be known before considering whether it can be avoided. Will the fatigue resistance of the repair be adequate? If the repair is in an area, which is highly stressed by fatigue, and particularly if the attempted repair is of a fatigue crack, inferior fatigue life can be expected unless the weld surface is ground smooth and no surface defects are left. Fillet welds, in which the root cannot be ground smooth, are not tolerable in areas of high fatigue stress.

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Will the repair resist its environment? Besides corrosion, it is important to consider the possibility of stress corrosion, corrosion fatigue, thermal fatigue and oxidation in service. Corrosion and oxidation resistance usually requires that the composition of the filler metal is at least as noble or oxidation resistant as the parent metal. For corrosion fatigue resistance, the repair weld profile may need to be smoothed. To resist stress corrosion, PWHT may be necessary to restore the correct microstructure, reduce hardness and reduce the residual stress left by the repair. Can the repair be inspected and tested? For onerous service, radiography and/or ultrasonic examination are often desirable, but problems are likely if stainless steel or nickel alloy filler is used; moreover, such repairs cannot be assessed by magnetic particle inspection. In such cases, it is particularly important to carry out the procedural tests for repairs very critically, to ensure that there are no risks of cracking and no likelihood of serious welder-induced defects. Indeed, for all repair welds, it is vital to ensure that the welders are properly motivated and carefully supervised. As-welded repairs Repair without PWHT is, of course, normal where the original weld was not heat treated, but some alloy steels and many thick-sectioned components require PWHT to maintain a reasonable level of toughness, corrosion resistance etc. However, PWHT of components in service is not always easy or even possible, and local PWHT may give rise to more problems than it solves except in simple structures.

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Repair Considerations  The first thing to consider, is it worth repairing?  Repair welding can cost up to ten times the original cost of making the weld, that’s if it all goes according to plan.  There could be access issues, contamination issues if it’s in service.  There could be metallurgical issues, changing properties etc.  It may be more cost efficient to replace the component or cut the weld out completely.  Try and establish the reason for defect occurrence as this may determine a change to the procedure or re training.  Was the defect due to poor fit up conditions, misalignment.

Weld Repairs Section 20

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Cost of Weld Repairs Original weld

Cost

Repair weld

Cut, prep, tack

£

Inspector Repair report (NCR etc)

££

Welder time

£

Inspector Identify repair area

££

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Repair Considerations

Extra cost

Consumable & gas

£

Inspector Mark out repair area

££

Visual inspection

£

Welder Remove defect

££

NDT

££

Inspector Visual inspection of excavation

££

Documentation

£

Inspector NDT area of excavation

££

Inspector Monitor repair welding

££

Welder time

£

Consumable & gas

£

Inspector Visual inspection

££

NDT

££

Extra repair Documentation

£

Penalty % NDT

££

 Can pre heat be tolerated.  Local pre heat and welding could lead to distortion and residual stress.  In service repairs more complex, electrical and combustible material issues, contamination.  Production repairs less complex.  Approved repair procedure and welder.  Mark accurately where material must be removed.

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Investigation What is the nature of the defect?  If the defect can be attributed to workmanship, it may not require further investigation.  However, if it is some form of cracking, it will require further investigation as the problem may be repeated during the repair.

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Investigation How was the defect detected?  Visual.  Dye Penetrant.  Magnetic particle.  Radiography.  Ultrasonics.  These processes are not always 100% accurate.  Human error etc.

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20‐1

Where is the Defect?  Defects found on the surface by a NDT method that is surface only, may require further investigation using sub surface NDT.  Remove defect and investigate further.  Internal defects will be found with UT or X-Ray.  UT, will be able to size and locate defect far better than X-Ray.

What is the Defect? The process can help determine defect?  A sub surface NDT method can help establish defect type with good interpretation.  Porosity tends to be central in the weld and at restarts and finishes.  Slag inclusions and lack of fusion defects tend to be between runs and at the side walls of the original preparation.

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What is the Defect?

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What is the Defect?

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Removing Material  Depending on the material, gouging, machining, filing, grinding can be used, pencil type de burrs for more intricate work.  A greater area than just the defect area will have to be removed to allow for access and promote good fusion characteristics.  If the depth of defect is not known, progressively remove material and NDT. check.

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Weld Repairs

Plan View of defect

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20‐2

Production Weld Repairs

Arc Air Gouging

Side view of defect excavation

D

Side view of repair welding

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Preparation of Weld Repairs  The shape of the repaired area is very important.  A boat type shape with large radius is preferred to allow good access and prevent any lack of fusion defects which could occur with straight edges.

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Considerations Before Welding  Pre heat, ref original procedure.  Distortion control measures, this could be quite dramatic as the heat concentration will generally be very localised.  Materials such as S/S may require back purging; pipes etc.  Process to use, TIG is probably the most versatile but there may be consumable match issues.

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Copyright © TWI Ltd

Preparation of Weld Repairs Ideal repair shape

Potential for lack of fusion defects

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Upon Completion  PWHT to remove residual stress and/or hydrogen release.  The repair may need dressing to give it the same geometry as the rest of the weld.  Inspection of finished repair including NDT as original process used.  Pressure testing if required.

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20‐3

Repairs You are working as a Senior Welding Inspector on a high pressure gas supply pipe line. The pipe has a wall thickness of 12mm and in certain areas 25mm. The pipe is a 24” longitudinal seamed X60 grade, welded with the SAW process. All circumferential seams are welded with an E6010 electrode for the root and hot pass, fillers and capping E8010 electrode, all passes in the PF position. Copyright © TWI Ltd

Question 2 While witnessing a weld repair on a circumferential welded joint, the fabricator uses a preheat of 200°C. Would this pre heat temperature be correct in accordance with the TWI Specification? a. No, only 75°C preheats shall be used b. Yes providing the original preheat applied to the circumferential joint was 200°C c. Yes, providing the original preheat applied to the circumferential joint was 125°C d. No, preheats aren’t permitted for repair welds on the circumferential seams Copyright © TWI Ltd

Question 4

Question 1 One of the circumferential seams has a linear slag inclusion 450mm in length and has been detected by radiography. Can this defect be repaired in accordance with the TWI Specification? a. This defect can be repaired providing the welding is conducted in the same direction as the original welding and under constant supervision b. Any defect exceeding 450mm in length cant be repaired in accordance with the TWI Specification c. This defect can be welded in accordance with the TWI specification, but must be welded using a basic type electrode and under constant supervision d. All options are incorrect Copyright © TWI Ltd

Question 3 One of your welding inspectors reports back to you that a weld repair has been removed using the arc air gouging process. Is this acceptable in accordance with the TWI Specification? a. No, defective areas shall be removed by thermal cutting, grinding back to clean metal and inspected by MPI before commencement of welding b. Yes, providing the gouged area is cleaned by grinding back to clean metal, inspected by PT before commencement of welding c. Yes, providing the gouged area is cleaned by grinding back to clean metal, then visual inspection before the commencement of welding d. All options are incorrect Copyright © TWI Ltd

Question 5

You notice that no weld repair procedures have been approved for this pipeline. In this situation would you permit any repairs to be conducted?

One of your inspectors reports back to you that a crack has been repaired in Weld 42, section 34. Which of the following statements are correct?

a. Yes, providing all weld repairs are conducted in accordance with the TWI Specification b. Yes, providing that all welders are qualified to conduct the repairs c. No, all repair welding shall have an approved welding repair procedure d. No, repairs aren’t generally conducted on pipelines; any defects detected would normally require the entire weld to be removed

a. This would not be permitted, as cracks can’t be repaired in accordance with the TWI Specification b. This would be permitted providing the crack didn’t exceed the maximum repairable defect length c. This would be permitted providing the repair has be carried out in accordance with the approved repair WPS d. A crack like defect can’t occur using the electrodes stated

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Copyright © TWI Ltd

20‐4

Question 6

Question 7

After conducting a repair a slag inclusion that exceeds the maximum permitted length has been detected by radiography. The fabricator requests approval from you to conduct a weld repair in this defective area. Would you permit this repair?

One of your welding inspectors informs you that a weld repair has been conducted without a qualified welding inspector present. In this situation which of the following applies?

a. Yes, a repair can be conducted on this type of defect in accordance with the TWI Specification b. No, weld repairs are not permitted in accordance with the TWI Specification c. The TWI Specification makes no reference to this situation; you would need to ask advice on this situation d. No, in this situation the entire weld would have to be removed, a cutout

a. This is not permitted by the TWI Specification b. Providing the welder is qualified this is acceptable in accordance with the TWI Specification c. Providing the welder informs you that the approved repair WPS has been strictly adhered to this is acceptable d. No options are correct

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Question 8 You suspect that lack of inter run fusion has occurred during the welding of one of the pipes to pipe circumferential seams. Which of the following NDT methods would best detect this defect a. MPI or DPI as this defect is usually surface breaking b. RT would be best suited to detect this defect if no slag was present c. UT would be best suited to detect this defect if no slag was present d. 2 options are correct Copyright © TWI Ltd

Copyright © TWI Ltd

Question 9 Some codes and standards only permit weld repairs to be conducted for a minimum amount of times before a full cut out is required. Why do you think this is the case? a. If a weld is repaired an unlimited amount of times it may affect the mechanical and metallurgical properties of the weld b. The amount of preheat will be too high for the welder to weld c. A critical post heat treat will always be required d. It would be difficult to find approved welders to conduct these type of repairs Copyright © TWI Ltd

Question 10 One of your welding inspectors asks you what is the minimum depth a weld repair excavation needs to be. Which of the following would be your answer? a. The thickness of the base material. b. As deep as it is required to ensure the defect has been fully removed c. The depth would depend on the radiography interpretation report d. 2 options are correct

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20‐5

Appendix 1 Homework

Senior Welding Inspection: Multiple Choice Questions Paper 1 Name: ……………………………….…………………………. Date: …………………… 1

Which is the best destructive test for showing lack of sidewall fusion in a 25mm thickness butt weld? a b c d

2

Which of the following would be cause for rejection by most fabrication standards when inspecting fillet welds with undercut, a small amount of? a b c d

3

EN EN EN EN

ISO 15614. ISO 2560. 287. ISO 17637.

Excess weld metal height. Start porosity. Spatter. Arc strikes.

Which of the following is a planar imperfection? a b c d

6

BS BS BS BS

When visually inspecting the face of a finished weld which of the following flaws would be considered the most serious: a b c d

5

Depth. Length. Width. Sharpness.

The European Standard for NDE of fusion welds by visual examination is: a b c d

4

Nick break. Side bend. Charpy impact. Face bend test.

Lack of sidewall fusion. Slag inclusion. Linear porosity. Root concavity.

A fillet weld has an actual throat thickness of 8mm and a leg length of 7mm, what is the excess weld metal? a b c d

2.1mm. 1.8mm. 3.1mm. 1.4mm.

WIS10-30816 Appendix 1–Paper 1

A1-1

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7

BS EN ISO 17637 allows the use of a magnifying glass for visual inspection, but recommends that the magnification is: a b c d

8

A WPS may specify a maximum width for individual weld beads (weave width) when welding C-Mn steels. If the width is exceeded it may cause: a b c d

9

Above the dashed line. Below the dashed line. Above the solid line. Below the solid line.

Which of the following elements is added to steel to give resistance to creep at elevated service temperatures? a b c d

13

Prevent linear porosity. Prevent burn-through. Prevent oxidation of the root bead. Eliminate moisture pick-up in the root bead.

According to AWS A2.4 a weld symbol for the other side is placed: a b c d

12

Tungsten spatter. Risk of crater cracking. Risk of arc strikes. Interpass temperature.

Pipe bores of some materials must be purged with argon before and during TIG welding to: a b c d

11

Lack of inter-run fusion. A reduction in HAZ toughness. Lack of sidewall fusion. Too low a deposition rate.

In TIG welding a current slope-out device reduces: a b c d

10

x2. x2 to x5. x5 to x10. Not greater than x20.

Nickel. Manganese. Molybdenum. Aluminium.

Compound welds: a Always contain full penetration butt welds. b Joints which have combinations of welds made by different welding processes. c Combinations between two different weld types. d All of the above.

WIS10-30816 Appendix 1–Paper 1

A1-2

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14

Welding inspectors: a b c d

15

In an arc welding process, which of the following is the correct term used for the amount of weld metal deposited per minute? a b c d

16

The material thickness reduces. Faster welding speeds. The use of a larger welding electrode. A reduction in carbon content in the parent material.

What is the maximum allowable linear misalignment for 8mm material if the code states the following, ‘Linear misalignment is permissible if the maximum dimension does not exceed 10% of t up to a maximum of 2mm’? a b c d

19

27.5mm. 24mm. 13.3mm. 12.5mm.

Pre-heat for steel will increase if: a b c d

18

Filling rate. Deposition rate. Weld deposition. Weld duty cycle.

The throat thickness of 19mm fillet weld is? a b c d

17

Normally supervise welders. Are normally requested to write welding procedures. Are sometimes requested to qualify welders. All of the above.

0.8mm. 2mm. 8mm. None of the above, insufficient information provided.

BS EN ISO 17637: a The minimum light illumination required for visual inspection is 350 Lux. b The minimum light illumination required for visual inspection is 500 Lux. c The minimum light illumination required for visual inspection is 600 Lux at not less than 30°. d Doesn’t specify any viewing conditions for visual inspection.

20

Which of the following electrodes and current types may be used for the TIG welding of nickel and its alloys? a b c d

Cerium electrode, DC –ve. Zirconium electrode, AC. Thorium electrode, DC +ve. All of the above may be used.

WIS10-30816 Appendix 1–Paper 1

A1-3

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21

When considering the MIG/MAG welding process which of the following metal transfer modes would be the most suited to the welding of thick plates over 25mm in PA. a b c d

22

When considering hydrogen, which of the following welding processes would produce the lowest levels in the completed weld? (under controlled conditions) a b c d

23

MMA. SAW. TIG. FCAW.

In steel the element with the greatest effect on hardness is: a b c d

24

Dip transfer. Pulse transfer. Spray transfer. Globular transfer.

Chromium. Manganese. Carbon. Nickel.

Brittle fractures: a The susceptibility in steels will increase with the formation of a fine grain structure. b The susceptibility in steels will increase with a reduction in the in-service temperature to sub-zero conditions. c The susceptibility in steels will increase with a slow cooling rate. d All of the above.

25

Which of the following steels is considered non-magnetic? a b c d

26

In a transverse tensile test brittleness would be indicated if: a b c d

27

18%Cr, 8%Ni. 2.25Cr 1Mo. 9%Cr,1Mo. 9%Ni.

There is a reduction in cross-section at the position of fracture. The fracture surface is flat and featureless but has a rough surface. Fracture occurred in the weld metal. The fracture face shows beach marks.

A STRA test is used to measure the: a b c d

Tensile strength of the welded joint. Level of residual stress in butt joints. Fracture toughness of the HAZ. Through-thickness ductility of a steel plate (the Z direction).

WIS10-30816 Appendix 1–Paper 1

A1-4

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28

A macrosection is particularly good for showing: a b c d

29

A suitable gas/gas mixture for GMAW of aluminium is: a b c d

30

The weld metal HAZ microstructure. Overlap. Joint hardness. Spatter.

100%CO2. 100% Argon. 80% argon + 20% CO2. 98% argon + 2% O2.

A crack running along the centreline of a weld bead could be caused by: a b c d

Use of damp flux. Lack of preheat. Arc voltage too high. Weld bead too deep and very narrow.

WIS10-30816 Appendix 1–Paper 1

A1-5

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Senior Welding Inspector: Multiple Choice Questions Paper 2 Name: ……………………………….…………………………. Date: …………………… 1

The maximum hardness in the HAZ of a steel will increase if: a b c d

2

Initiation of a TIG arc using a high frequency spark may not be allowed because it: a b c d

3

Often causes tungsten inclusions. Can damage electronic equipment. Is an electrical safety hazard. Often causes stop/start porosity.

In friction welding, the metal at the interface when the joining occurs is described as being in the: a b c d

4

Heat input is increased. CEV is increased. Joint thickness is decreased. Basic electrodes are used.

Liquid state. Intercritical state. Plastic state. Elastic state.

What four criteria are necessary to produce hydrogen induced cold cracking? a Hydrogen, moisture, martensitic grain structure and heat. b Hydrogen, poor weld profiles, temperatures above 200oC and a slow cooling rate. c Hydrogen, a grain structure susceptible to cracking, stress and a temperature below 300oC. d Hydrogen, existing weld defects, stress and a grain structure susceptible to cracking.

5

Austenitic stainless steels are more susceptible to distortion when compared to ferritic steels this is because: a b c d

6

High coefficient of thermal expansion, low thermal conductivity. High coefficient of thermal expansion, high thermal conductivity. Low coefficient of thermal expansion, high thermal conductivity. Low coefficient thermal expansion, low thermal conductivity.

Transverse tensile test: a b c d

Is used to measure the ultimate tensile strength of the joint. Is used to measure the elongation of a material. Is used to measure the yield strength of a material. All of the above.

WIS10-300816 Appendix 1–Paper 2

A1-1

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7

In the welding of austenitic stainless steels, the electrode and plate materials are often specified to be low carbon content. The reason for this: a b c d

8

Essential variable: a b c d

9

Creates problems when welding in position (vertical, horizontal, overhead). Requires more heat to melt it when compared with aluminium. Increases weld pool fluidity. Decreases weld pool fluidity.

A welder qualified in the PG position would normally be qualified for welding: a b c d

13

Voltage. Amperage. Polarity. Both a and b.

An undesirable property of aluminium oxide residue is that it: a b c d

12

44%. 144%. 69.4%. 2.27%.

Which of the following will vary the most when varying the arc length using the MMA welding process? a b c d

11

In a WPS may change the properties of the weld. In a WPS may influence the visual acceptance. In a WPS may require re-approval of a weld procedure. All of the above.

In an all weld metal tensile test, the original test specimens gauge length is 50mm. After testing the gauge length increased to 72mm, what is the elongation percentage? a b c d

10

To prevent the formation of cracks in the HAZ. To prevent the formation of chromium carbides. To prevent cracking in the weld. Minimise distortion.

All diameters of pipe. Welding positions PA, PC, PG, and PF. In position PG only. All pipe wall thickness.

A fabrication calls for the toes to be blended in by grinding.The most likely reason for this is to… a b c d

Make the weld suitable for liquid (dye) penetrant inspection Improve the fatigue life reduce residual stresses improvethe general appearance of the welds

WIS10-300816 Appendix 1–Paper 2

A1-2

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14

A carbon equivalent of 0.48%: a b c d

15

Is Is Is Is

high for carbon steel and may require a preheat temperature over 100oC. insignificant for carbon steel and preheat will not be required. calculated from the heat-input formula. not a consideration for determining preheating temperatures.

Which of the following statements is true? a The core wire of an MMA electrode always contains alloying elements. b Basic electrodes are preferred when welding is carried out in situations where porosity free welds are specified. c Rutile electrodes always contain a large proportion of iron powder. d Cellulose electrodes may deposit in excess of 90ml of hydrogen per 100g of weld metal.

16

Preheat: a b c d

17

Which element has the greatest effect on general corrosion resistance? a b c d

18

2.16 kJ/mm. 0.036 kJ/mm. 2.61 kJ/mm. 0.36 kJ/mm.

Which of the following mechanical test(s) can give a quantitative measurement of ductility? a b c d

20

Manganese. Chromium. Carbon. Nickel.

Which of the following is the correct arc energy if the amps are 350, volts 32 and travel speed 310 mm/minute. a b c d

19

Must always be carried out on steels. Need not be carried out if post weld heat is to follow. Is always carried out using gas flames. None of the above.

Tensile test. Bend test Nick break test. Both a and b.

Which of the following are applicable to fatigue cracking? a b c d

A rough randomly torn fracture surface, an initiation point and beach marks. A smooth fracture surface, an initiation point and beach marks. Beach marks, step like appearance and a secondary mode of failure. All of the above.

WIS10-300816 Appendix 1–Paper 2

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21

22

Which of the following weld symbols in accordance with BS EN ISO 2553 represents a fillet weld made on the other side? a

b

c

d

What is a lap in steel? a b c d

23

24

A A A A

fold occurring in the steel during forming or rolling. sub-surface lamination, which may affect the strength of the steel. type of crack occurring in the parent material. non-metallic inclusion.

In accordance with BS EN ISO 2553 which of the following symbol best represents a double J butt weld? a

b

c

d

Which of the following welding symbols would indicate the depth of penetration in accordance with BS EN ISO 2553?

a

c

WIS10-300816 Appendix 1–Paper 2

z10

b

s10

d

10s

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25

How can you tell the difference between an EN/ISO weld symbol and an AWS weld symbol? a The EN/ISO weld symbol will always have the arrow side weld at the top of the reference line. b The EN/ISO symbol has the welds elementary symbol placed on the indication line lying above or below the solid reference line to indicate a weld on the other side. c The EN/ISO symbol has a fillet weld leg length identified by the letter ‘a’. d The EN/ISO symbol has a fillet weld throat thickness identified by the letter ‘z’.

26

What would the number 141 placed at the end of the reference line indicate on a welding symbol in accordance with BS EN ISO 2553? a b c d

27

What would the number 136 placed at the end of the reference line indicate on a welding symbol in accordance with BS EN ISO 2553? a b c d

28

MMA welding process. MIG welding process. FCAW welding process. MAG welding process.

What is meant by the term normative document? a b c d

29

NDT requirements. SAW welding process. MMA welding process. TIG welding process.

General term used to cover standards, specifications etc. A legal document, the requirements of which must be carried out. A document approved by a recognised body through consensus. A written description of all essential parameters for a given process.

In the AWS standard for welding symbols which of the following is true. a The elementary welding symbol is always place below the reference line to indicate a site weld. b The elementary welding symbol is always placed above the reference line to indicate a weld made on the arrow side. c The elementary welding symbol can be placed above or below the reference line to indicate a weld made on the other side. d The elementary welding symbol is always placed below the reference line to indicate a weld made on the arrow side.

30

Impact test: a b c d

Is a destructive test used to measure weld zone hardness. Is a mechanical test used to determine a welds resistance to creep. Is a dynamic test, which is used to give a measure of notch toughness. All of the above.

WIS10-300816 Appendix 1–Paper 2

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Senior Welding Inspector: Multiple Choice Questions Paper 3 Name: ……………………………….…………………………. Date: …………………… 1

If arc strikes are found on carbon steel (carbon equivalent of 0.5%), what undesirable grain structure may be present? a b c d

2

Which of the following units is used to express the energy absorbed by a charpy specimen? a b c d

3

Have Have Have Have

a a a a

lower heat input and a higher degree of grain refinement. lower heat input and a coarse grain structure. lower amount of distortion and a higher degree of grain refinement. higher amount of distortion and a lower degree of grain refinement.

Which of the following would you expect of a martensitic grain structure? a b c d

6

70 N/mm2 minimum UTS. 70N/mm2 minimum impact strength. 70,000 p.s.i. minimum UTS. 70,000 p.s.i. minimum yield strength.

A multi-run MMA butt weld made on low alloy steel consists of 5 passes using a 6mm diameter electrode, a 12 pass weld made on the same joint using a 4mm diameter electrode on the same material will: a b c d

5

Joules. Newton’s. Mega Pascal’s. Both a and c.

What does the 70 represent on an E7010 AWS A5.1 classified electrode? a b c d

4

Perlite. Martensite. Ferrite. All of the above are undesirable grain structures in constructional steels.

An An An An

increase increase increase increase

in in in in

toughness and a reduction in hardness. hardness and a reduction in ductility. ductility and a reduction in toughness. malleability and an increase in hardness.

Which of the following would reduce the chances of arc blow? a b c d

A A A A

change change change change

WIS10-30816 Appendix 1–Paper 3

from from from from

AC current to DC current. DC current to AC current. DC electrode +ve to DC electrode –ve. DC electrode –ve to DC electrode +ve.

A1-1

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7

Which of the following mechanical properties of a weld made on C-Mn steel is most affected if the heat input per unit length is excessively high? a b c d

8

Which of the following tests would you not expect to be carried out on a welder qualification test? a b c d

9

Se 75. Tm 170. Yb 169 Co 60.

When carrying out inspection on a Double V butt weld (35° bevel angle), which of the following NDT methods would be the most suited for the detection of lack of sidewall fusion in the root region? a b c d

13

Tesla. Lux. Hertz. Gray.

If it was a requirement to radiograph a 10mm thick steel weldment, which of the following isotopes would be the most suited with regards to application and quality? a b c d

12

Density and contrast. Sensitivity and definition. Density and sensitivity. Contrast and definition.

What are the units used when measuring light intensities for viewing test specimens using MPI or DPI testing? a b c d

11

Radiography. Tensile test. Macro. Bend test.

Which two aspects of radiographic images are normally measured? a b c d

10

Tensile strength. Ductility. Toughness. Elongation.

Ultrasonic Inspection. Radiographic Inspection. Magnetic Particle Inspection. Dye Penetrant Inspection.

Which NDT method would you associate with prods? a b c d

Radiographic Inspection. Magnetic Particle Inspection. Ultrasonic Inspection. Dye Penetrant Inspection..

WIS10-30816 Appendix 1–Paper 3

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14

When conducting DPI, which of the following are critical considerations? a b c d

15

Which material would be the least effective for DPI? a b c d

16

It can only be used on material over 3mm thickness. It can only detect surface defects. It can only be used on ferrous materials. Both b and c.

What is the main purpose of an IQI when used in Radiography? a b c d

20

The same as that required for visual inspection. 350 lux minimum, 500 lux recommended. 500 lux. Not specified, it’s left to the decision of the NDT technician.

A major disadvantage of MPI is: a b c d

19

If the component being tested is too large for regular inks to be used. During the inspection of components underwater. During the inspection of hot components. Iron powder is preferred over regular MPI inks due to the higher sensitivity achieved and ease of application.

During MPI inspection using contrast inks, what is the minimum light intensity requirements in accordance with the EN standards? a b c d

18

Carbon Manganese steels. 316L steel. Cast Iron. Both a and c.

Why might Iron powder be used when conducting MPI? a b c d

17

Thickness of component being tested. Weld preparation details. Components test temperature. All of the above.

To To To All

measure defect sensitivity. assess the smallest defect which can be detected. measure Radiographic sensitivity. of the above.

Back step welding is used to reduce: a b c d

Distortion. Stress corrosion cracking. Fatigue failure. Solidification cracking.

WIS10-30816 Appendix 1–Paper 3

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21

Which of the following materials will show the greatest amount of distortion, assuming heat inputs, material thickness etc. are the same? a b c d

22

HICC may occur due to which of the following? a b c d

23

use use use use

of of of of

a large bevel angle. basic coated electrodes. small diameter electrodes, maximise the number of weld passes. large diameter electrodes, minimise the number of weld passes.

Check incoming materials. Check and monitor consumable handling and storage. Check calibration certificates. Measure and monitor residual stress.

The inclusion of the inductance in the welding circuit when using the MIG/MAG welding process is to: a b c d

27

The The The The

A duty not normally undertaken by a Senior Welding Inspector: a b c d

26

The use of E6010 or E6011 electrodes. Keeping preheat to a minimum. The maintenance of minimum heat inputs. None of the above.

Distortion can be reduced by: a b c d

25

Damp electrodes. Lack of preheat. The presence of sulphur. Both a and b.

The likelihood of hydrogen cracking in a carbon steel weld can be reduced by: a b c d

24

High tensile strength C/Mn steel. Mild steel. 316L steel. QT steel.

Control the rate of spatter in the dip transfer mode. Control the rate of spatter in the spray transfer mode. It enables the welder to weld in position at higher current values. Both a and b.

What is ‘weld decay’? a A localised reduction in chromium content caused by sulphur and chromium combining in SS. b A localised reduction in chromium content caused by iron and chromium combining in SS. c A localised reduction in chromium content caused by carbon and chromium combining in SS. d A reduction in tensile strength of a material operating at elevated temperatures under a constant load, which generally leads to a failure of the component in SS.

WIS10-30816 Appendix 1–Paper 3

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28

What are the possible effects of having the heat input too low during welding? a b c d

29

Which of the following Isotopes may be used for a 25mm thick steel pipe to pipe weld DWSI (in accordance to BS EN ISO 17636-1)? a b c d

30

Low toughness, entrapped hydrogen and low hardness. High hardness, lack of fusion and entrapped hydrogen. Entrapped hydrogen, low toughness and high ductility. Lack of fusion, low toughness and a reduction in ductility.

Ir 192. Co 60. Se 75. Yb 169.

During a the welding of a test piece for the purpose of approving a WPS the following parameters have been recorded: Amps 300, Volts 32, ROL 210mm, time 1 minute. What is the arc energy value? a b c d

4.1 KJ/mm. 7.38 KJ/mm. 6.4 KJ/mm. 2.74 KJ/mm.

WIS10-30816 Appendix 1–Paper 3

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Senior Welding Inspector: Multiple Choice Questions Paper 4 Name: ……………………………….…………………………. Date: ……………………

Magnetic Particle Testing (MT) 1

Which of the following materials cannot be tested using MT? a b c d

2

Suspending magnetic particles in a liquid has the advantage of: a b c d

3

Flaw is at right angles to the direction of the current. Flaw is parallel to the magnetic flux. Flaw is at right angles to the magnetic flux. Current is at right angles to the magnetic flux.

When MPI is performed with fluorescent ink, the maximum level of white light illumination that must be present at the area under inspection is: a b c d

6

Iron oxide. Ferrous sulphate. Aluminium oxide. A special high nickel alloy

Maximum sensitivity in MT is achieved when the: a b c d

5

Making the same amount of detection media go further. Improving particle mobility. Preventing corrosion. Improving contrast.

Magnetic particles for use in magnetic ink are generally made from: a b c d

4

Cobalt. Nickel. Carbon steel. Brass.

50 lux. 500 lux 2000 microwatts per square millimetre. 20 lux.

Which of the following statements about the use of permanent magnets for MT is true? a b c d

They require no power supply. They are ideal for use with dry magnetic particles. They provide excellent sensitivity for surface breaking defects. They give the clearest indications of discontinuities lying parallel to a line joining the magnet poles.

WIS10-30816 Appendix 1–Paper 4

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Copyright © TWI Ltd

7

The region in the neighbourhood of a permanent magnet or current carrying device in which magnetic forces exist is called a: a b c d

8

The general name given to a simple device used in MPI to indicate field strength and direction is: a b c d

9

Flux indicator. Gauss meter. Magnetometer. Dynamometer.

The flash point of a solvent is: a b c d

10

Magnetic circuit. Magnetic field. Leakage field. Magnetic pole.

The temperature above which there is a danger of spontaneous combustion of the solvent vapour. It's boiling point. The temperature below which there is a danger of spontaneous combustion of the solvent vapour. The temperature above which the solvent becomes soluble in water.

The temperature above which a ferromagnetic material becomes nonmagnetic is called the: a b c d

Breaking point. Curie point. Sharp point. Turning point.

Penetrant Testing (PT) 11

A disadvantage of penetrant flaw detection is that: a b c d

12

An advantage of penetrant flaw detection is that: a b c d

13

It can only detect surface breaking discontinuities. It cannot be used on fine cracks such as fatigue cracks. Parts cannot be re-tested. It cannot be used on non-ferrous materials.

It can be used on non-ferromagnetic materials. Fluorescent penetrant can be used for on-site testing of large parts. The temperature of the part need not be considered. Painted parts can be rapidly tested.

European national codes and standards do not normally permit the penetrant method to be used outside what temperature range? a b c d

10-55 C. 15-50 C. 10-50 C. 5-60 C.

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Copyright © TWI Ltd

14

An advantage of colour contrast penetrants over fluorescent penetrants is that they: a b c d

15

Are more sensitive because the indications are easier to see. Do not require special removers. Are more suitable for smooth surfaces. Do not require an electrical power supply.

Typically, when fluorescent penetrants are used: a The inspector should allow a few minutes before starting inspection to allow night vision to develop. b The quantity of white light in the inspection booth should be limited to around 20lux. c Removal of excess penetrant is monitored under UV-A light. d All of the above.

16

Which of the following discontinuities would be impossible to detect using the penetrant method? a b c d

17

When selecting which penetrant system to employ which of the following factors must be considered? a b c d

18

Forging laps. Grinding cracks. Non-metallic internal inclusions. Crater cracks.

Component surface finish. The sensitivity required. The compatibility of the penetrant with the material under inspection. All of the above must be considered.

Which of the following statements concerning liquid penetrant testing is correct? a Fluorescent penetrants will produce red against white discontinuity indications. b Non-fluorescent penetrants require the use of black lights. c Yellow-green fluorescent indications glow in the dark for easy viewing and interpretation. d Fluorescent penetrants produce yellow green visible light under UV-A illumination.

19

Development time is influenced by the: a b c d

20

Type of penetrant used. Type of developer used. Temperature of the material being tested. All of the above.

Factors that affect the rate of penetration include: a b c d

Surface temperature. Surface condition & cleanliness. Viscosity. All of the above.

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Copyright © TWI Ltd

Ultrasonic Testing (UT) 21

The process of comparing an instrument or device with a standard is called: a b c d

22

The piezoelectric material in a probe, which vibrates to produce ultrasonic waves, is called a: a b c d

23

Water. Oil. Gylcerin Any of the above.

The primary purpose of reference blocks is: a b c d

27

Filter undesirable reflections from the specimen. Tune transducer to the correct operating frequency. Reduce attenuation within the specimen. Transmit ultrasonic waves from the transducer to the specimen.

A couplant can be: a b c d

26

Scanning. Attenuation. Angulating. Resonating.

The purpose of a couplant is to: a b c d

25

Backing material. Lucite wedge. Transducer element or crystal. Couplant.

Moving a probe over a test surface either manually or automatically is referred to as: a b c d

24

Angulation. Calibration. Attenuation. Correlation.

To aid the operator in obtaining maximum back reflection. To obtain the greatest sensitivity possible from an instrument. To obtain a common reproducible reference standard. None of the above is correct.

The gradual loss of energy as ultrasonic vibrations travel through a material is referred to as: a b c d

Attention. Attendance. Attemperation. Attenuation.

WIS10-30816 Appendix 1–Paper 4

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Copyright © TWI Ltd

28

Any condition that causes reflection of ultrasound in pulse echo testing can be referred to as: a b c d

29

If the cap of a single V (60° included angle) full penetration butt-weld is ground flush 0 degree compression probe is useful for: a b c d

30

A dispenser. A discontinuity. An attenuator. A refractor.

Detecting lack of side wall fusion. Detecting lack of root fusion. Assessing excess penetration. All of the above.

Welds in austenitic stainless steel: a Are easily tested by ultrasonic methods. b Are difficult to test by ultrasonic methods due to the coarse grain structure of the weld deposit. c Are difficult to test by ultrasonic methods due to the highly attenuating parent material. d Both b and c are correct.

Radiographic Testing (RT) 31

The two factors that most affect the sensitivity of a radiograph are: a b c d

32

The instrument used to measure film density is called: a b c d

33

A A A A

densitometer. photometer. radiometer. proportional counter.

Compared with conventional ultrasonic testing one advantage of film radiography is: a b c d

34

Density and unsharpness. Latitude and grain size. Density and latitude. Contrast and definition.

It's cheaper. A permanent record is directly produced. Lack of fusion is easily detected. All of the above are significant advantages.

Which of the following weld defects is most reliably detected by radiography? a b c d

Porosity. Lack of inter-run fusion. Lack of root fusion. Heat affected zone crack.

WIS10-30816 Appendix 1–Paper 4

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Copyright © TWI Ltd

35

Which of the following weld defects is least reliably detected by radiography? a b c d

36

Radiography is a reliable method for the detection of: a b c d

37

Porosity. Slag inclusion. Lack of penetration. Heat affected zone crack.

Volumetric flaws. Planar flaws. Both volumetric and planar flaws. Laminations in rolled steel products.

DWDI radiography is usually limited to girth welds in pipe with an outside diameter of (consider EN ISO standard): a b c d

75mm or less. 80mm or less. 85mm or less. 100mm or less.

38

Radiography is best suited for: a Cruciform joints. b Dissimilar welds. c T butt welds. d Set through joints

39

The correct terminology for the image that forms on a radiographic film during exposure to radiation is: a b c d

40

Ghost image. Latent image. Patent image. Spitting image.

If detected by radiography undercut appears as: a

A very thin, continuous or intermittent, straight dark line running parallel with the edge of the weld cap. b A broad straight edged image towards the centre of the weld image. c A dark line of variable width, continuous or intermittent, between the weld & parent material & following the contour of the edge of the weld cap or root. d A dark irregular image, within the weld image, continuous or intermittent, of variable width and film density running essentially parallel to the weld axis

WIS10-30816 Appendix 1–Paper 4

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Copyright © TWI Ltd

Appendix 2 Training Reports

CSWIP 3.2 TRAINING  REPORT MT 01 INSPECTION COMPANY:  TWI NDT

REPORT NUMBER: 01   PROJECT NUMBER: 1970

CLIENT: Tramcar 

WELD NUMBER: 48

SPECIFICATION: TWI NDT specification

WELD DETAILS: Single V butt weld  weld number  SURFACE CONDITION: As welded

    TECHNIQUE 132/T PROCEDURE NUMBER: 132

WELDING PROCESS: 111

DATE OF EXAMINATION: 4.8.15

SCOPE OF INSPECTION: 100% of weld and HAZ

LOCATION: Prenton Park workshop

PROCESS STAGE: After PWHT

MATERIAL:ASTM 182

LIFT TEST COMPLETED: YES @ 5.4 KG

CONSUMABLES

   MANUFACTURER    

TYPE

BATCH NUMBERS

Solvent based ink

   Magnaflux 

7HF

120514

Contrast Paint

   Magnaflux 

WCP‐2

150415

Solvent Remover

   Magnaflux

SKC‐S

140905

TESTING TECHNIQUE: AC Yoke TEMPERATURE:Ambient  LIGHT LEVELS: >350Lux at test surface      TEST SENSITIVITY: 3 indications, Burmah castrol strip CURRENT TYPE: DC POLE SPACING: 50 mm TEST RESULTS: No defects detected No reportable  indications detected

ACTION: No further actions 

OPERATORS NAME: S Jones

REPORT DATE: 4.8.15

OPERATORS SIGNATURE:   SJones

OPERATORS QUALIFICATION: CSWIP Level 2 MPI

SJ Training  MT01 

CSWIP 3.2 TRAINING REPORT PT 01 INSPECTION COMPANY:  TWI NDT

REPORT NUMBER: 0011   PROJECT NUMBER: 1970

CLIENT: Tramcar 

WELD NUMBER: 69

SPECIFICATION: CSWIP

WELD DETAILS: Single V Butt joint weld  SURFACE CONDITION: As welded

    TECHNIQUE 132/PT PROCEDURE NUMBER: 132

WELDING PROCESS: 141

DATE OF EXAMINATION: 8.4.15

SCOPE OF INSPECTION: 100%

LOCATION: Prenton Park workshop

PROCESS STAGE: Completed

MATERIAL:316 SS

VIEWING CONDITIONS: >500Lux

   CONSUMABLES

MANUFACTURER

TYPE

BATCH NUMBERS

Solvent Remover

   Magnaflux 

7HF

120514

Penetrant

   Magnaflux 

SKL‐SP2

150415

    Developer

  Magnaflow

SKC‐S

140905

APPLICATION: Brush DWELL TIME: 20 minutes DEVELOPMENT TIME: 10 minutes TEST TEMPERATURE:  5‐10 oC TEST RESULTS

ACTIONS

SIGNATURE:  

D Pennar

   NAME: Dye Pennar

SJ Training PT1

REPORT DATE: 8.4.15

    QUALIFICATION: CSWIP LT2 PT (ISO 9712)

CSWIP 3.2 TTRAINING REPORT RT 01 DATE OF INSPECTION: 4.8.15

INSPECTION COMPANY: TWI NDT

REPORT NUMBER: 1970

   CLIENT:

WELDING PROCESS: MMA 111

Tramcar

WELD REFERENCE: 47    SURFACE CONDITION: As welded MMA 111

JOINT GEOMETRY

TEST PROCEDURE: 131 STAGE OF TEST: After PWHT 25mm 2.5mm

SCOPE OF INSPECTION: 100% MATERIAL: 

‐ Bevel Angle 30o + 5o, ‐ 0o ‐ Root Gap 2.5mm. ‐ Plate thickness 30 mm ‐Weld Length

C‐Mn

Source Strength: 60 Ci

FFD/SFD: 150 mm

KV's: N/A

mA's: N/A

Screen type: Pb

Exposure: 4Ci mins

Focal Spot: 

Source Size: 2x2

FILM TYPE: AGFA D4 

IQI TYPE: Fe

DEVELOPMENT: 4 mins @ 20oC manual

FIXING CONDITIONS 6 mins @ 20oC

RADIOGRAPHIC TECHNIQUE: SWSI

ISOTOPE TYPE: Ir 192

TEST RESULTS FILM ID

SEN %

DENSITY

COMMENTS

ACTION

1‐2

2%

2‐3

No defects observed

Accept

2‐3

2%

2‐3

No defects observed

Accept

3‐4

2%

2‐3

No defects observed

Accept

4‐5

2%

2‐3

No defects observed

Accept

5‐6

2%

2‐3

lack of root penetration

Reject

TEST LIMITATIONS:

TEST OPERATOR: Sjones SIGNATURE: S Jones

SJ Training  RT01

REPORT DATE: 4.8.15

OPERATORS QUALIFICATION: CSWIP L2 RT (EN ISO9712)

CSWIP TRAINING  REPORT UT01 INSPECTION COMPANY: TWI NDT

CLIENT: Tramcar

PROJECT NUMBER: 267

REPORT NUMBER:256

PROJECT LOCATION: Prenton Workshop

DATE OF INSPECTION: 4.8.15

JOINT GEOMETRY

SCOPE OF INSPECTION: 100%

WELD NUMBER:24

MATERIAL: Aluminium 5083 DIMENSIONS:   700mm L         FORM:Plate 25mm 2mm

SURFACE CONDITION: As welded

    WPS: 0069  GTAW           TEMPERATURE :Ambient TEST PROCEDURE: 14 − Root Gap 2mm. − Root to be inspected by MT before commencment  of next weld pass

DETECTION UNIT: KSM         SERIAL NUMBER:6754 COUPLANT: Sonagel

   CALIBRATION BLOCKS: V1,V2 SIZE

 PROBES

SENSITIVITY

SCANNING

5 MHz 0O Compression

10mm Twin Crystal

BWE 80% F.S.H At test  depth

At test sensitivity

O 4 MHz 45  Shear

10mm Single Crystal

80% F.S.H  1.5mm Hole

At test sensitivity

4 MHz 60  Shear

10mm Single Crystal

80% F.S.H  1.5mm Hole

At test sensitivity

O 4 MHz 70  Shear

10mm Single Crystal

80% F.S.H  1.5mm Hole

At test sensitivity

O

TEST RESULTS:  BS EN ISO 17640:2010 1. Crack like indication detected with 60o shear wave scanning in root location. 2. Slag inclusions detected with 45o shear wave scanning

ACCEPTANCE:TWI NDT SPECIFICATION Not accptabe

NAME:

M Rogers

LEVEL OF QUALIFICATION: CSWIP L2 UT EN ISO 9712

SJ training UT01

SIGNATURE:  REPORT DATE: 4.8.15

Senior Welding Inspector: Training Reports Questions

Name: ……………………………….…………………………. Date: ……………………

MT01 Questions 1

The lift test stated in MT01 a b c d

2

Do you consider the scanning pattern shown to be a b c d

3

b c d

Yes, as so long as you have valid eye test and have completed competency checks Yes, it states a minimum of 350 Lux but recommends 500 Lux No, 350 Lux is for black light not white light No, 500 Lux is the minimum permitted light intensity

Which of the following statements is correct? a b c d

5

Correct and fully compliant with the procedure Missing the dimensions for each span of the yoke conducted Incorrect and not compliant with the specification This type of scanning is only applicable to AC

In relation to the light levels reported on MT01, is it stated correctly and which is the correct statement? a

4

Is not required if test sensitivity is recorded Complies with specification and is common practice Lift testing is for permanent magnets only Does not comply with the specification

Pole Pole Pole Pole

spacing spacing spacing spacing

is 300mm minimum is 300mm maximum is 150mm maximum depends on the power of the Yoke

Which of the following statements is correct? a AC Yokes only shall be reported b DC yokes shall be used in all situations c According to the TWI specification DC shall be used on raw materials but not welds d Permanent magnets shall be used on live plant and AC on non-live plant

WIS10-30816 Appendix 2 – Questions

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Copyright © TWI Ltd

PT01 Questions 6

In accordance with the TWI specification, at which of the following temperatures is penetrant inspection permissible a b c d

7

Do you consider the development time stated in PT01 as a b c d

8

Acceptable to the TWI specification as no maximum is stated Not acceptable to the TWI specification A suitable period as to compliment the dwell time All options are incorrect

In accordance with the TWI Specification is the material type stated on PT01 acceptable a b c d

9

Between 1°C and10°C Between 5°C and 10°C Between 5°C and 50°C d. Between 25°C and 40°C

Yes it is acceptable No, only non-ferrous based materials can be inspected by DPI It is not specified in the TWI Specification regarding this material so I would accept No, Duplex and aluminum are acceptable but the material stated is unacceptable

In accordance with TWI Specification are the viewing conditions acceptable as stated in PT01 a b c d

Acceptable if used for the TAM calibration Yes the conditions are acceptable No the conditions are not acceptable Acceptable when doing fluorescent

10 In accordance with the TWI Specification are the consumable manufacturers acceptable to the TWI specification a b c d

Yes, they are acceptable No, they are not acceptable The developer and penetrant only are acceptable to the specification The developer and remover only are acceptable to the specification

WIS10-30816 Appendix 2 – Questions

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Copyright © TWI Ltd

RT01 Questions 11 On Radiographic Inspection report RT 01, is the operator’s qualification acceptable to the TWI specification? a b c d

Yes No This acceptable if the qualification to ISO 17636 has been verified This is not acceptable because the level 2 is only a minimum

12 Is the material stated on RT 01? a b c d

Not permissible in the TWI specification Not possible to radiograph due to its permeability Not possible to radiograph due to its high density Well suited to radiography and is acceptable to the TWI specification

13 Is the scope of inspection reported on RT 01 acceptable to the TWI specification? a b c d

If that’s all that’s accessible then yes No The specification only calls for 10% radiography on project 7690 All options are incorrect

14 In relation to the fixing conditions stated on RT 01 a b c d

The time and temperatures stated are correct The time is ok but the temperature is too high The temperature is ok but the time is too long All options are incorrect

15 In relation to the Development stated on RT 01 a b c d

The time and temperatures stated are correct The time is ok but the temperature is too low The temperature is ok but the time is too long All options are incorrect

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Copyright © TWI Ltd

UT01 Questions 16 Do the calibration blocks shown on UT 01 comply with the requirements of the TWI specification? a b c d

The calibration blocks stated are specification compliant The blocks do not matter providing a resolution check is completed The calibration blocks stated are not specification compliant ONLY if a cross checker is present at calibration shall the specification allow the use of the V1,V2 blocks stated

17 Is it possible to use the 60 reported defect 1? a b c d

o

shear probe as reported in UT 01 to scan for the

No Yes Only the crack like indication ,would be discovered It is possible if you scan at 40 o to the probe angle itself

18 According to the TWI specification, Is the material stated on report UT 01 acceptable for ultrasonic examination a b c d

Yes it is acceptable to the specification with no special requirements. There is no mention of Aluminum in the specification Yes, ultrasonic testing is often used on Aluminum welds If the attenuation check is done then this material can be inspected by UT with company approval

19 In relation to the joint geometry stated on report UT 01 a b c d

A 6 dB drop should be referenced here The report should state the bevel angle/included angle There would be sufficient information to conduct successfully A trained operator would know his beam path

ultrasonic

testing

20 How many probes would be used on a 25mm single V butt weld in accordance with the TWI specification? a b c d

Only a zero degree would be required for this joint 4 probes would be required 3 probes would be required All options are feasible if you have access to both sides of the joint

WIS10-30816 Appendix 2 – Questions

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Copyright © TWI Ltd

Appendix 3 Training Drawing

7

8

Nozzle 450 dia with 20mm flange.

2

10,000

4

1

Nozzles 50mm dia with 10mm flanges

Drawing one CSWIP 3.2 weld symbols training  

2000mm dia

3

6

5

Nozzle 600mm with 40mm flange.

Appendix 4 Specification Questions  

Senior Welding Inspector: Specification Questions

Name: ……………………………….…………………………. Date: ……………………

1.

The symbols s and ≤ refer to :a) Plate thickness and arrow side b) Nominal throat thickness and less than c) Nominal butt weld thickness and less than and equal to d) Single sided and vee butt weld with reinforcement removed

2.

In the case of a ferrous double sided butt weld, which inspection methods should be employed before the second side is welded. a) Dye penetrant and MPI b) Visual only under magnification of x5 c) Visual and dye penetrant d) Visual and MPI

3.

What would be the largest leg length dimensions and the smallest throat dimension of a fillet weld deposited on 12mm thick plates. a) 12mm leg length, 8.4mm throat b) 15mm leg length, 10.5mm throat c) 14mm leg length, 9.8mm throat d) 15mm leg length, 8.4mm throat

4.

An arc strike has been removed by grinding and the inspection has proven acceptable. The thickness of the joint is 25mm and the removal depth 1mm deep. Is this acceptable? a) There is no problem with 1mm as 2mm is acceptable b) This is not acceptable as no reduction in thickness is allowed c) Not acceptable as 0.5mm is the maximum reduction in thickness d) As long as the inspection proved acceptable this would be allowable

5.

Continuous Sub arc welding is being conducted on the manufacture of large I beams 15m in length. After completion of each I beam, the re cycled flux approximately 5kg in weight has another 5kg of new flux added before the operation continues again. Is this allowable? a) No only new flux can be used b) This is not required as the system has a filtration system built in c) This combination of mixing new and used is adequate d) It depends if the operation is hydrogen controlled or not

WIS10-30816 Appendix 4 – Questions

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Copyright © TWI Ltd

6.

Ultrasonic testing of a circumferential pipe butt weld 200mm diameter and 25mm thick, has detected lack of fusion 180mm in length. The contractor has a repair procedure and wants to carry out a repair. What would be your course of action? a) If it’s a first repair and the procedure is being followed, this would be allowable b) If a qualified inspector witnessed the repair this would be allowable c) You should not allow this to happen until you witness a repeat of the NDT d) You should insist on a complete cut out

7.

The following parameters were used on a 10mm thick austinetic stainless steel butt weld using the TIG process, 12 volts, 180 amps and a travel speed of 40mm per minute. Witnessing this operation, what would be your course of action? a) The heat input is too high so stop the operation b) The heat input is too low so stop the operation c) As long as the welding procedure is adhered to, continue the operation d) No options are correct

8.

A procedure was conducted in the PF position with MMA in 15mm thick C Mn steel. The following tests were conducted, hardness, macro, side bends, tensile, and impacts. Which of the following statements is correct? a) The procedure can be used in any position b) The procedure can only be used in the original test position c) The procedure can be used in the PA, PB, PC and PF positions d) The procedure can be used in the PC, PF and PD positions

9.

A quenched and tempered steel has to undergo Post Weld Heat Treatment. Which of the following is correct? a) b) c) d)

10.

Heating rate controlled from 320°c, soak temperature 590°c, controlled to 320°c and thermocouples removed at 110°c Heating rate controlled from 300°c, soak temperature 580°c, controlled to 300°c and thermocouples removed below 110°c Heating rate controlled from 220°c, soak temperature 450°c, controlled to 220°c and removal of thermocouples at this point Heating rate controlled to a soak temperature of 700°c, controlled to ambient at which point thermocouples removed.

cooling rate cooling rate cooling rate cooling rate

A quenched and tempered steel 40mm thick requires pre heating at a temperature of 100°c and a controlled interpass temperature of 100°c. the SAW process id being used. The heat input must be controlled. Which of the following conforms? a) b) c) d)

28 32 32 32

volts, volts, volts, volts,

WIS10-30816 Appendix 4 – Questions

450 650 620 750

amps, amps, amps, amps,

travel travel travel travel

speed speed speed speed

650mm per min 400mm per min 350 mm per min 800 mm per min

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Copyright © TWI Ltd